Fox tailing can be caused by genetics or stress.
In the case of genetics, it is expressed on the whole plant generally [ as you have described with lower buds also showing signs].
It is when stressors cause fox tailing that the fox tail may be less potent than the other 'mature' buds.
The reason being the trichomes are not fully developed due to their late appearance.
This article seems to cover much of what I just said.
Decode cannabis foxtailing. Learn to distinguish desirable genetic growth from damaging stress signals and manage your crop effectively.
biologyinsights.com
Your plants look really good~!
Do you lower/decrease your lights power through flowering?
To me not doing that would be one of the main reasons for fox tailing when not genetic.
I have never had fox tailing although I seem to have had many other issues even just recently.
Possibly turning down the lights and letting the fox tailed plant go longer will help with the trichomes.