As far as I know and can find, it's like this in the FIG Elite code
For a standard full/multiple turn with free leg in optional position:
- "Have a fixed and well defined shape throughout the turn."
I would personally say any shape for this would/should be allowed, so long as you hold the exact position throughout the turn. However, I can imagine judges seeing certain positions as "mistakes" and taking precision deductions. For example, if you have your free leg in a forwards passe shape, but with your foot well past your knee behind you, or just a little below the knee, maybe some judges see that as a mistake. With the position gymgirl 84 describes it couuuld be seen as a failed back attitude if you have bad luck?
If the shape you mean is as gymgirl84 describes... I think technically it should be allowed, but it might take some judges by surprise. Especially on lower levels, judges may be used to seeing the same thing 1000 times, and then suddenly see your turn shape and hold a little deliberation, to be like "ehm, guys, is that allowed? Does any of you know?".
I also wonder if it's wise to learn it in that shape. It feels like such a hard position to keep consistent with good core tension, not arching your back. As somebody with a solid double/tripple turn on floor and working on doubles on beam... I would not. Then again, I have stiff hip flexors and I've never properly learned or taught turns so what do I know, haha.
In short:
Should be allowed in FIG elite code, but risk of deductions due to misinterpretation. Might also just not be the must practical shape for progression.