Dennis you are all over the place and your issue really hasn't changed in any of the many threads you now have going on the same topic.
If you hear "crunching", you have movement. Plain and simple.
If the floor structure is suitable and the subfloor material is thick enough then the problem comes down to the installation method used.
You keep trying to nail-down a trowel size and your waisting your time chasing that tail. There is also nothing wrong with the thinset you have mentioned, so forget about that.
Your problem is your installer and the methods he is using.
I had another tiling company come out and he said he never puts less than 1/4- 1/2 thinset between wood flooring and cement backer board.
THAT is some more hokey crap. A 1/4" X 1/4" X 1/4" trowel is recommended for the cement board. That trowel DOES NOT leave you with 1/4" of thinset after the board is put down. To say he puts down a 1/2" of thinset is just plain not true and that's more BS. If he had a 1/2" of thinset under the boards he wouldn't be able to nail the boards down and they would be rolling all over the place. Where do you find these guys.
Should it have polymers for flexing and correct size. Jaz commented on my other tiling project 1/4 between cement and wood boards ? Is 1/8 flat out incorrect ?
This is a good example of why you should use only one thread and not start a new thread every time you have a notion. Where are the comments by jaz that you now refer to? In which thread do I find those comments?
Just because a thinset is "polymer modified" doesn't mean it is flexible like you think it is flexible. Polymer modified thinset is still as hard as concrete. Polymer modified thinset does not allow you to use an inept installer either. Your installation should be fine using the products you have used so forget about that aspect.
If your floor is crunching it will not last. My guess is there is no thinset under the cement board. Until you can provide more detailed information we can't help you with your issues. I would suggest you stop believing everything your being told by guys that either want your business or have delivered you substandard workmanship. Don't be a fool.
Is 1/8 flat out incorrect ?
Is 1/8" WHAT incorrect? What are you talking about?