If you want a number, I would say no more than 30-50 meters. In an open area, that's about the limit of targeting anyway, so I think it works out well.
As for explaining things like walls and such...it's all about angles.
If you want maximum range, simple ballistics say that you need to take off at about a 45 degree angle. If you're standing next to a wall, you don't have that luxury, so your take-off angle is going to be much steeper, thereby reducing your range.
Again, this is not "flight"...more like a long, magically-assisted jump.