I've never had a rabbit escape over a 30" tall pen.
Well, that makes one of us.
Back when I lived in San Antonio, I had a 2x3x6 grid (w/l/h) condo connected to a permanent run made of two 48'' high x-pens that took up my whole living room. One day, I came out of my bedroom to find Nala on the wrong side of the pen! Naturally, I assumed she had snuck out past me earlier when I opened one of the "door" panels to go in and out of their pen for whatever reason. I played a less-than-fun game of "hide and go screw yourself"(the condo and one wall of the pen were mere inches from a built-in entertainment center and couldn't be moved - she just ran back and forth thwarting me as I repeatedly went around through the kitchen to get to the far side) before finally catching her and locking her back up.
The next night, I'm going to the kitchen... and AGAIN, she is on the WRONG SIDE of the x-pen!! This time, I
know it wasn't human error. I was stumped! Another long chase scene and she was back in the pen. I couldn't figure out how on earth she was getting out, so I made a post here asking for help that resulted in
an entire page of speculation, lol.
The next night, I finally left my room at *exactly* the right time to catch her right in the middle of a third escape. This little 4.5 month old lionhead was
climbing the corner where the x-pen met the NIC grid condo! She was 3/4 of the way to freedom, but her surprise at getting caught caused her to slide back down into the pen. The solution turned out to be zip-tying a piece of poster board to the top of the x-pen on the one panel where she was able to climb. That way, she'd get halfway up and have no more footholds on one side. After that, she never managed to climb out again.
If you're worried about jumping specifically, I've had Nala jump out of a 28'' pen (actually, it was made with NIC grids and was 2 grids high) but above about 30-32'' you're usually safe as long as there's no toys or boxes to climb on and you don't have a true Houdini bunny.
Smaller breeds (again, so I've read) can jump higher than the larger breeds. The giant breeds have too much weight, perhaps.
I have also always heard this and in my experience, it seems to be true. Smaller bunns are more agile than the large or giant ones.