OK, I've had to redo the shims as I'd really stuffed far too much in there & I had the screws underneath done up so tight that I felt the column would shoot off into the ceiling if it was done up any tighter, I could see the baseboard starting to curl, I swear..... indeed one of the bolts has been totally burred inside so the allen key won't work & can't be removed.... so, I've redone it as best I can, all things considered, conservatively doing up the 3 remaining adjustable bolts this time, and I have the red dot showing just 1 or maybe 2mm off from dead-centre target........... I mean, that's not bad, is it???