Hi, Vagabond and welcome to PR.

Reading your original question, I might be able to give some relavant experience for you.

I bought a Benbo in the late '80's and it still remains my main tripod. Yeah it can drift on slippery (tile) surfaces if you press down on it. But for actual macro field work (and I have done some of that ) when you are on uneven, natural surfaces, I've never had a drifting problem. And I've used it with my Bronica ETRS medium format camera with 200mm lens with an extension tube in between. I still use it on tile surfaces with my digital SLR for interior work.

If you are serious about macro work, the Benbo (or Uni-Loc) can't be beat. In fact, I haven't even looked for another tripod since I bought it so I don't know what else is out there.

I have never used the tripod to mount the camera on the bottom of center column. But I have had the legs in all manner of positions to get low and close.

It may not seem as utterly stable as some others out there. But remember, with proper technique (i.e. never using those "intermediate" shutter speeds between 1/8s to 1/60s, using a cable/remote shutter release, using mirror lockup, etc.), flexibility over brute stability out in the field may be the key to success.