Thank you for your feedback. We do state in words, diagrams and videos, that you have to allow an overlap on the edge of the frame, depending on the width of magnetic tape you are using. In this case, with panels less than 1m2, we would supply the 12.5mm tape. Therefore, you add 12.5mm each side which adds 25mm in total to the size of the panel if you measure the internal dimension first.
I apologise if there has been any confusion!
Regards
Richard Cutts