Stealing air is a major danger in military jumping; where one parachutist's canopy drifts under another. This causes the higher jumper's canopy to collapse momentarily. At altitude this isn't a problem - once a canopy is open; it stays open. It flutters, then pops open again while the jumper goes whizzing by you shouting yooouuuu priiiicccckkkkk......
It's when it happens close to the ground it becomes real dangerous - I've got a pair of rebuilt knees that speak to that. 
Ram-air chutes work a bit differently. Rather than cup air, creating drag to slow a parachutist's descent; ram-airs work by forming an airfoil. For ram-airs; the danger zone is directly behind and just above. You can fly directly above and below quite comfortably. When you approach the formation you do so in a diving arc from the sides if you're good; or sliding in sideways if you're learning.
15,000ft max. Ram-airs are unstable much above that altitude and there's breathing to consider. The jumpers would've been dropped in a hop'pop - that is; open as soon as you leave the aircraft. That would give plenty of time - relatively speaking, of course - to get into formation if you're flying conservatively.I'd hate to imagine how high the jump was in order to get 80 skydivers in that formation. There are no rookies in that formation. It takes incredible skill to control a chute like that.
Good Lord; what a superb demonstration that was though - the choreography was brilliant. CRW was never my thing - I've only got about 70-80 CRW jumps; most of my (civilian) skydiving experience was RW - freefall formation. It's waaaaaaay easier; and much less risky. I've always had a 'thing' about canopies - I like 'em just fine when they're nice and safe above me.
