You probably need a complete different workflow for a more realistic result. One approach would be to represent the t-shirt as a real 3D model and then project the design elements as so called “decals” on the t-shirts surface.
Hey, not sure if this is due to a render order update behind the scenes but do you notice now that the decals change order depending on the camera angle when a few are overlapping? Was this was managed differently in the past?
The shirt as 3D model might be one solution, but honestly not very practical especially if there are many products that might also change from time to time.
Also since colors are fixed and not a free choice there isn’t much a full 3D model benefits customers, since the print is frontal. It would be different for more complex shapes like hats.
However a good visual result can be archived by only modelling the front depth mesh of the shirt, the folds and bend deformations and transparent blend it with the original picture. Additionally i would adapt the lighting setup with the scene and have the same picture with an actual print in all the print-techniques used to figure the visual appearance differences with the actual printed quality/appearance, so the result does not look like a digital overlay but convincing real.
I saw 2 shirt print services before that offer this kind of preview which is highly valuable for customers as this is exactly what customers really only care about how the result will look in real life. It differs a lot between printing techniques and products + the scene lighting of the photo.
The basic implementation is trivial, it’s mostly just individual work you need to do such as creating the surface mesh of each photo pose/product you need, you might as well pre-extract it from the luminance of the photo first in your modelling tool, but it needs manual adjustment since brightness as height isn’t 100% correct and you want those UV deformations as you would expect on the shirt.