Lines on vinyl when pressing over seams

I'm pressing over the arm seem when doing a sleeve press and on one hoodie I pressed had a line down the middle of the vinyl from the seam.

Just wondering what people do to help this issue?

I've heard of people using cusions (think that's what they were called) basically an insert placed in the sleeve. If I use an insert is there a recommended material or would something as simple as cardboard work in this situation?

Any suggestions would be most welcome.

Thanks