finally worked out what I did wrong today, when I calculated the break angle in the body, I was off by 2.5mm, now it all makes sense, I didn't include the thickness of the base plate, hopefully on the next build I'll get that part right.

this is a bit embarrasing to admit but I realised the truss rod wasn't set right, no wonder the action was so high, it was set with a huge amount of backbow, so now it's setup up and neck almost straight the action is down to 1.5mm at the low E, I don't have to lower the bridge anymore, it feels much better to play now, lesson learnt.