It's a math problem beside others. Keeping the frame inside the picture at all times and avoiding crashes with "rectangular surface outside drawing area" is a pain in the ass.
It becomes a lot worse if I allow moving the frame with the mouse "somehow". How exactly is also a good question. Drag&drop sucks, click on spot which will be used as frame center might work, but you will almost always have to use the arrows to fine tune.
There is already a button for tripple frame with one click. But it has problems too, because checking for all three areas if they are inside the image is a pain, so it's not done right now.
All in all it's one of those things where you get too little benefit for far too much effort, so I didn't improve it further until now.
EDIT:
I have added the functionality to use the mouse to center the frame and the mouse scroll wheel to increase/decrease the frame size.
Also When you hover the mouse over the "T" (tripple frame) button, two additional frames will be shown, left and right of main frame to give you an idea what you will get from the tripple frame function.