How to determine if a Gui Frame is obstructing another Frame?

I apologize if the title is a little vague, wasnt too sure how to word it.

Essentially what I want to do is run checks to see if the size of this selected box frame is filling the entire “defender” frame
Screenshot_2
Keep in mind the box can be at any given position within the defender frame

How would I go about doing this?

Does the “box frame” change width during manipulation? I assume you mean to check if it’s X is >= Defender.X and it’s Y >= Defender.Y?

if box.AbsoluteSize.X >= Defender.AbsoluteSize.X and box.AbsoluteSize.Y >= Defender.AbsoluteSize.Y then
--It is covering the whole Defender
else
-- it isn't covering the whole Defender

That might work for you.