still not sure why on a long print the resin doesn't cure and get thick and gloopy.
Surely even the scattered light from the projector will thicken the nearby resin.
Does it have a particular light intensity threshhold ?

Also could you use one of the new mini-led projectors around and just put it nearer ?
Or even direct it directly at the base of the vat ? all you'd need would be Longer legs on the printer and a bracket to hold the projector.

£750 (ish) for the projector seems a lot to me :-) (but I am permanently lacking money)