I know it mt be little late into your project but have you consider using a pre-formed shower tray with the falls already in it then adjust your floor level to suit the tray afterwards
Hi Andy, I did consider it but I wanted a simple linear fall to an infinity drain. Even if I had used a former to do this I would still be in the same situation now unless I had levelled the floor beforehand.
Sadly I am too far in now and need to correct from this point 🙁
Is it a possibility you could adhere ditra matting to gain just enough height and feather it in with bal rapid set. Obviously giving the backer board a good primer first