7" isn't very high for a sleeping box. My nethie crosses would struggle to be comfortable in a small space, unless it was a tunnel with open ends. Have you considered making it a little taller (say 12") - most rabbits are bigger than mine and once full of hay, you still need room for bunny.
As others have said, most buns can jump quite high - certainly 2' (the height of a sofa or step-over barrier) with no problems, if they want to. I have had some that would clear 4' easily.
Well done for the forward planning - and it's fun to make bunny stuff yourself.