ufh prep

hi lads I'm getting conflicting advice from fballs and a few others so I will ask you.
New concrete base so needs dpm
customer wants ufh matting under camero so what's best prep .
balls said 1200 then dpm then 300
but isn't 1200 a lower compression than 300 . also doesn't it need a fibre screed for ufh.

 

Cant you dpm prime then 700?

 

Sod that...leave it to dry, 10mm of 1200 or 300. Leave for a few days then fit