i think of the double eyed split tail friction hitches we
use as all very similar; this giving a key to easily remembering them.
They all employ a top coil (4 uninterrupted turns around host lifeline)
that will give pretty sure stop, but too powerfully so might bind. So we
precede them with another choking grab (except VT family uses a gauntlet
of braids to bend lifeline like rappelling rack to not pass full loading
to the coil) to limit loading to the coil and keep it in it's productive
powerband of slide and grip without seizing.
A Distel just takes the leg to top of the coil, and brings it below to serve this previous grab that buffers loading to the coil. A Schwab simply reverses this grab; so that a Distel is kinda like a 4/1 Clove, while a Schwab is a 4/1 Cow type configurations. The self tending class of hitches, take 1 leg as buffer similarly, but then also that choke tightens down on the other leg too, so that the loading to the coil is buffered at the top and bottom of the coil, and just not to 1 leg of the coil. Without this innovation, the hitch seems to grab when moving up and needs to be tended by hand or device.