I have followed your question because is concerning some polyamides that are less known by comparison to traditional ones (PA 6,6; PA 6; PA 11 and PA 12, others)!
My suggestion is to follow the scientific literature and to try to find a minimum of information regarding the thermal characterizations by DSC of PA6,9 and PA 6,8!
To help a little, please consider for 100% crystalline PA 6,9 an enthalpy of fusion of 257 J/g !