The bug
When adding the Invisible
tag to item frames the item inside becomes smaller.
How to reproduce
Place two item frames with large items inside them, e.g. glass panes
/data modify entity @e[type=item_frame,sort=nearest,limit=1] Invisible set value 1b
As far as I can say, there is no difference size. Frame shifts on screen due to perspective, since invisible frame is shifted 1/16 closed to block.