Sister Romeo not cutting to size

New to all this but getting by ok, however we have an issue and don’t seem to be able to find anything settings wise that I might be able to change to help.

Width is cutting to size but height is out by quite a bit.

Basic vinyl;
If I cut a 100mm square, the height is around 96mm
If I cut a 200mm square, the height is around 191mm
Width is perfect

Can anyone point me in the right direction to correct this?