We have 180 people to photograph and 6 steps to stand on. There is enough room for all but who goes on the top row the tallest or shortest? How to best arrange everyone?
In my opinion, do not force sorting by height. People are supposed to have fun during the photo. People choose a place next to a friend or a group of friends, next to the crush; probably they arrived earlier to be at the center.
Focusing on comparing heights will be chaos... ChAoSs.
You can define some categories tho. Women at the bottom and men at the top? Especially if they are sitting on a bench. The directive board at the bottom? First graders?
You need to focus on 180 people! ...really, you need to worry about more important things than height.
Give clear instructions. Carry a megaphone. Start filling from the center to the edges to maximize a general composition.
Have two assistants, one for the left and one for the right, but only for implementing your centralized instructions; make them wear perhaps a colorful vest, so the instructions they give have a bit of authority.
Solve any technical stuff before organizing people. An assistant should solve any minor incident that presents, not you. Only focus on giving instructions.
One thing that could be height-related is if the angle to the camera is too narrow because you are using a short focal length (A), then some short people on the back (4), could be covered by another (3). You could ask for the taller men to be in the far row.
(A few could get a box... LotR reference)
You could consider a longer focal length (B) or position the camera at a higher position (C).
Steven Kersting's advice of taking several shoots is a must. One instruction that you can give is that people stand comfortably but do not move their bodies at a given moment. Changes in the face and expressions are inevitable.
The other general advice is that the odd rows align to the middle of the even rows and vice-versa. So the faces will be in the gap of the two people in front of them.
Try to find the perfect, and I mean the perfect spot for the camera. The perpendicular line that forms with the stairs needs to be the center, if not, you will have parallelism problems, for example, people start looking smaller on the left vs the right, or the supposed horizontal lines could end up being convergent, and therefore inclined.
P.S. If you do not need to use the 6 steps, and the composition is good enough on, let's say 5, go for it. In my opinion odd numbers, 5 rows is better than 6, but if your categories need it, for example, it is a graduation ceremony of even numbers of women and men, 6 is ok.
Tallest in the middle; shortest to the sides... the steps only keep people of the same height equally visible.
Also, not part of the question, but I suggest taking the images in small bursts; and plenty of them. That increases the chance of getting more people looking decent (not blinking/etc); and more source images for compositing...
Based on the comment, one possibility is to put the people at the bottom of the stairs, and take the photo from the top of the stairs. Will works even better with a balcony or window of tall building.
Extrapolating above you can use drone and make photo (almost) from the top (air). Of course you should make people to look in this direction.
Ladder and chalk.
Arrive early and figure out where you want to take the photo from, which will define the background and overall lighting by the time everyone's ready.
Then climb the ladder and estimate the edges of your shot. With 6 steps and 180 people that's 30 per row, or 15 either side of centerline.
Spacing of half a metre per person means the middle row will be 15 metres wide. That likely needs shoulder-forward posing. 50cm might be a little close, depending on culture etc.
If the steps are deep enough, you might get multiple rows of people per-step.
Its also likely there will be more space at the rear because its a big sector, so expect some of the shy people to gravitate to the rear. In balance, the front row will be shorter, so fewer people there.
Specifically consider the leaders / speakers / core people, and position them in the front row or dead center. Also find if anyone's in a wheelchair or needs a cane or similar and make sure there's a space for them in an accessible place.
Use the chalk to lay out a boarder on the ground, and when people arrive tell them to "stand within the lines" People will always spread out too wide, so a line helps.
When on the ladder, pick the worst pairings and briefly say "Tall guy in the cool red hat, can you move to the other side" or whatever it takes. Aim to fix the worst 2~3 things that catch your eye.
Always take several shots back-to-back quickly. You might have to `shop someone's face from one image to another if they blink or sneeze. Getting 180 people to smile at once is unlikely, just do your best. Every pro photographer has a patter to help with this.
Also consider a tidy sign-board for someone to hold; "Class of `67 Reunion, December 2023" or whatever the group is.
Depending on what you want to achieve, the answer is either "average distribution" or "tall & short".
Average distribution - if all you want to use is 6 steps and 6 rows of people, and there is enough space horizontally to fit them all, just ask people to form on the steps without sorting. If someone happens to be tall enough to obscure people behind them, move them around until everyone is seen.
Tall & Short - 180 is a lot of people and 6 steps may not be enough. Get all the tallest people and ask them to form a seventh row on top of the steps. They are tall and will easily stick out behind the original 6th row. On the bottom of the stairs, ask all the short people to form a row before the original first row - they are short and so will not obscure people behind them. If needed, you can even form additional rows in front by having people kneel or sit.