Put the original points mag back on to prove a point just incase you're chasing the wrong end of the stick.
I think you could move the timing around a bit from 2.9 & it would still rev regardless. The factory setting of 2.9 isn't an exact setting as in how high it revs--within reason,--but if you went back to 2mm it might sound like its struggling to rev out as its getting a bit retarded--a bit like me lol--& now i've forgotten the rest of the story!!.
Ok looking back you have a 250 so 3.2 btdc is factory, but if Rex's say 2.9 they must have variations built into the electronics for when it running. Be interesting to strobe to a mark with a felt pen & see if it moves to advance more or retards at revs--or whatever!!.