FYI - OK - Finally got it adjusted. It turns out there is a small allen screw on the bottom of the boom in addition to the 2 bolts mentioned in the instructions. The allen screw is not obvious until you view things from the side. It's protruding head prevented the boom from being shortened any further. Removing this allen screw allowed the boom to be pushed into the frame as needed.
Very poor instructions for this provided by HP Velo,IMO. I have run into other annuying niggles not mentioned in the manual as well. But that's a story for another time. Right now, the frustrations I'm experiencing has me questioning whether I made the right purchase for me. Hopefully I'll feel better about as time goes on.