Couple of points, don't get caught up on the terms such as fixed, anchor, floating etc, etc. as being definitive, they are descriptive of an idea, rather being the idea.
Nothing is complicating anything Fenwick, above is the very point you are taking to heart. It is about "floating thumb" not touching fingers.
Like I said there are two simple ways to look at how you set your hands in relation to your thumbs, which is what the thread is about, which is why any anchor would be about the thumb.....not fingers, after all the elbow could be seen as a fixed point as the forearm moves from its fixed point as it runs along the bass....in that case any part that touches the body is then a fixed point if we want to take it all literal surely?
Height of instrument comes in to it, as does design, but the point being made is the line of the forearm though the wrist and the implication of fixing the thumb means the wrist must flex to allow the fingers to drop to reach he D and G strings on a four string bass.
If playing low gives you that.....job done.
If you bass design gives you this.....job done.
If your own personal idiosyncratic style gives you this....job done.
If anyone has their forearm and wrist in line job done, what ever anyone does relating to how they play, forearm and wrist in line is the way forward.
If this cannot be achieved all the time, then look to achieve it for most of the time. Like I said, do not get caught up in the terminology, this is the web and English is not everyone's first language, for those that do not speak or understand English, all the terminology is meaningless.
That is why there is a lot of hand movement and gestures in those videos, so a certain level of understanding can be gained from just watching them.....no sound required.
Fergie.