It seems like something that could be improved by 3d printing.

I’m guessing that if a vet has to assist several animals of the same species maybe it could be possible to get some kind of mask that could fit most of them.

Although I’m not sure if that’s something that would help or maybe it will just be more cumbersome.

Are the lines on the side of the print or on the top? Do they appear always on the same spots?

Try printing small callibration pieces, to see if it always happens

https://www.thingiverse.com/thing:4707289 https://www.tableflipfoundry.com/3d-printing/the-cones-of-calibration-v3/

https://ameralabs.com/blog/town-calibration-part/

From the picture it seems that you need to change your fep sheet. When you look at the fep does the lines coincide with the marks it has?