Controlled parachute rolls are great for training, but I can assure you and I do speak from experience, that landing under a normal (not a sporty thing) parachute is more akin to the proverbial "sack of spuds".
Vital to keep the legs together and bent, which is why the ground trg. has its place. Worth remembering that 20 knots would be above limits for airborne forces static line jumps, and that nil wind is not preferable. About 8kts is just perfect for a PX4 - not sure about Mr Baker's silken devices - I guess at that stage in the process you don't really care.
Also much easier jumping at night - the comparative lack of visual clues is an advantage.
How many on this board have stepped out - ie left a non-viable aircraft that was not fitted with a seat? A stude and his instructor at RN EFTS in 1979 had to leave their Dog. Stude landed sunnyside in the cow meadow, QFI finished easy-over in the slurry pit...