I am still at 3.1, but had a go at this for fun (do not have any convenient setup for 3.2).
The first two reps were quite though: I did not hit head or neck, but the impact was not soft. On the mat it was simply annoying, on grass would have been pretty hard. Then I realised that getting more horizontal speed by pressing harder with the hands and "closing" more into the roll helps a lot. The other reps felt much better. I have practised a bit more and now I think I could even do on grass -haven't tried though. Having to push more and put slightly more energy was a bit counterintuitive at first: one would think that the slower/softer you go the better, but that seems not to be the case. Any further advice on this? Thanks!