Not only are you not 2ding after the second loop, but you're also not holding forward, and therefore tao keeps flying back, resulting in a dropped combo.
A technique that may remedy this (I say may because everyone plays differently), is to go to 2d~6 -> 236b -> 512d~36bbbbbb. Your motion in your "loop" is from what I see all entirely 3's and 6's. Thats not good. You need to make it slower, and you need to input the 2.
Also another factor is the angle you're holding your joystick/controller. It happens to me sometimes.
If you want I can just make a short video on how I do it
1. There is no reason you should be looking for highest damage potential for hexaedge, and instead, just look for moves gatling into hexaedge at all. This is because for the most part if you get a sweet hit with a possible high damage combo (eg. 6c CH), what would you rather do, TLx12 for 6k+ easy? or into Hexaedge for like 3k or something? The only reason I use hexaedge is- 1) Tao's only DP. Once she hits 50 meter she now has an OPTION to get out of pressure, and a fully finished hexaedge is a good oki position. 2)To finish the enemy off, with out worrying about them bursting. All super's and throw's (until the followup hit) is unburstable.
2. I dont understand the question you're looking for a tauntloop/non tauntloop... ender... not mid/only corner..?
3. 6b CH goes into 5b combo's easy. 6b normal hit can hexaedge i think. I never really use it, because tao's mixup sucks. Instead, go into more pressure/mixup by 236b -> j.5d~b after or something creative.