all depending where I put the tripod that holds it
Ok I think the answer is... change where you put the tripod that holds it.
But I assume this is limited due the total space between the model and the background.
If you increase the distance between the model and the background you have space to put the flash directly behind the model. Experiment with distances, for example if your model is 1.5 mts tall, put your model 1.5 mts away from the background and the flash just behind. Try other distances for example 1.5x or 2x the height of the model.
This distance also helps reducing the reflected light to wrap arround your model.
Aditionally very important!:
Change the zoom range on the flash to the smallest number. That makes the light spread more.
Pull the little transparent grid the flash itself has and leave it infront of the flash strobe.
Use the flash in the same orientation as your image.
You can also use a pice of vegetal paper in front of the flash.
As you are using the flash exactly behind the subject you can not have an umbrella.
If you want to use an umbrella you need more than one.
One important thing is that you can not use a very wide lens... Imagine you want to shoot with a fish lens, of course at 2 mts you can not have an even backdrop. Try to use at least 50mm lens. The longer the better.
You need first of all to learn how to take a photo of a simple white background with no model. The result is a pretty boring white photo, but you need to know it.
This distance afects the total brightness of the background. Start for example at 1/32 the total power of the flash.
At 1.5 mts away and 1/16 I can blow a white background at f5.6. Iso 400 (rough estimation).
So you have room to play: f/8? use 1/8. f/11? Use 1/4.
It is also important that your background is white and diffusive.
A coated paper or plastic is NOT good. This makes hotspots and the edges look gray.