Oh no I'm considering the side, however we also need to consider that it is not going to be entirely smooth, there will be small bumps to provide some short-lived aerial velocity, however there may also be angled protrusions causing a directional drift to slow the person down further.

The way the person initially falls could also contribute, whether they're upright, trying to land on their feet at first, or simple falling to the side, or backwards, etc.
As the bones break they can break in positions which could affect the direction they continue to roll, if they hit the angled protrusions mentioned earlier, and possibly even latch for a moment.

If they're going at a slow speed, perhaps they can make a guess towards a small bump to increase the time spent airborne? This may speed things up but the air friction may play a role in how long the person stays up there (large or slim).

I'm thinking about this a bit too much.