This is honestly a gray area that I haven't seen discussed. I'm surprised it wasn't brought up when Mania came out, either. Tails has similar behavior there.
This needs an open discussion, but imo this type of Tails control should be made explicitly legal as opposed to the typical 2P control.
And in the case of Mania (Not S12013 for obvious reasons) I'd suggest that flying as S+T should be perfectly legal.
I think in the case of Mania, this wasn't really an issue because there was no glitch with S+T where they earn credit twice for one ring while flying together, so there wasn't a need to ban the use of flying together as S+T, whereas here in S1 2013 it exists to prevent players from doubling as many rings as they can.
CyberScore's rule on this reads "Flying as Sonic & Tails in such a way as to obtain credit twice for any single ring is disallowed."
Essentially, you can still fly as S+T, but if you earn credit twice for a single ring, your run is nullified. It does allow for more possibilities as Sonic (like 155 Marble 3) but it also seems more difficult to enforce without video proof, although I suppose the 1st place mandatory video proof rule can take care of that, but I'm not sure how strictly it's enforced.
I'm personally fine with banning flying as S+T together completely, because it makes sense why the rule exists, but I also feel like a runner shouldn't be punished for accidentally grabbing onto Tails and jumping off without collecting any rings when they were trying to set something up and failed to avoid grabbing onto him, as I've done many times in practice on GHZ 1 and Scrap Brain 3, where I was experimenting with a possible technique similar to my GHZ 1 technique here to top Sonic's long standing 123 rings record.
Had to reset many times due to briefly flying as S+T together in recording my GHZ 1 run to showcase for this thread. It doesn't look that hard, but if Tails is right on top of you when you put him into flight, you're pretty much guaranteed to grab onto him.
>_> that's why I was usually trying to move around and put him into flight simultaneously.