One of the reasons gymnastics is a difficult sport is how the athlete perceives what it takes to do a skill and what they think they're doing vs what they're really doing. Think about that for a day or two and see if you may be thinking yourself right out of the best solutions for skills that have you puzzled, because you know something..... but don't.
Geez, I can't seem to get all the way around on my standing bhs. Hmm, maybe if I throw my head earlier I'll have enough of a "head" start to make it around all the way.
Rats, I'm still not making it even though I'm trying as hard as I can to get it around. I'll just have to keep trying and get better at throwing my head and chest around.
So that's a pretty common problem that needs to be over come when a beginner is trying to learn a bhs. They're so darn certain they have it figured out and know what they're doing, that they completely over look any suggestion that doesn't fit their model of how it should be done and resist opinion about what their attempt looks like.
In other words.... You may think you can't see the floor until 3/4, but I'll bet you it's more like a bit before vertical. If you see the floor a bit before vertical you'll take 3/100 of a second (or there abouts) to react and do anything that make the twist happen. By the time you complete your reaction process you'll be just past vertical and have plenty of time to twist. Maybe not a 2/1, but odds are that you'll begin to anticipate "seeing the floor" and will start your twist when you're about 1/4 to 1/3 of the way into your layout.
The tendency is to anticipate and go earlier over a period of months. That's why you have it, and then lose it. Get it straightened out doing the "see the floor" thing and when you get it figured out do another 150-200 (no, not in one week) before adding more twist. Once you get that far into the process you'll need to have days where you limit your work to seeing the floor and doing only a full. Maybe one day with fulls, and one day with full+, then one day with fulls and two days with full+.... repeat that pattern for a very long time.... like 8-12 months, or 1600 tumble runs portioned out as described above.