My preference, and only because I understand it, is to teach a set from a forward lean that "stands up" in mid-air followed by the upper body "falling" into the beginnining of the lay-out......so it's forward-up-over into the somersault. The lead arm of the twist reaches back and down as the "up phase" ends and the "over" phase starts and points to the floor at about a 1/8 turnr. I don't teach the "point" to the floor but that's the way it looks.
The lead arm pulls in and to the lead side as the lay-out begins, and the follow arm pulls in and tries to catch up as the skill rotates.
It looks like the girl in the pic is working it this way, and with a 3/4 twist is at the point of bringing the follow arm in to catch up with the lead arm. Both arms will be held in tighter to the body for the remainder of the twist.
The exact arm position of each gymnast I've taught follows this general guide line, but each athlete has a slight variation to account for their unique qualities of weight distribution, tumble speed, snap down timing and distance, set angle, and number of twists.