If you have guides to align shoulders/lower edge and possibly the center of the t-shirt, you don't need to play with opacity to align on a model. I don't know PS, but with Gimp:
There is an ofn-preset-guides script to create custom guides with a single keystroke
There is an ofn-file-next script that does "Save & close current image, open next" that can ...
You are either using the profile incorrectly/in the wrong place, or it is a bad/broken profile.
If you set it as the monitor's profile in system display settings it is a bad profile. If you are selecting it elsewhere, such as for softproofing, you are using it incorrectly.
From the comments:
If you show me an alogrithm capable doing this, I am more than happy to automate it.
For a software approach I would try to use OpenPose, a deep-learning based human posture tracking stack.
They have pre-packaged builds so you don't need to recompile anything yourself. You just need to download the neural network model, put stuff in ...