I haven't seen a ride height difference with changes in the air preload of the stock shocks.
The hitting the mount first thing has been mentioned since forever. Doubt HD cares at this point. Crappy deal.
I notice a TINY bit of movement when I add air to my SG, but I don't think it is enough to change ride height at all.
Also, to the OP, how smooth was the course? I know that they are typically very smooth, but with the lower than recommended air in the shocks with 320 pounds on the bike a small bump would cause more drop than desired while in a corner.
It is normal that some bike mods can change behaviors of the bike in a particular situation. Good for you that you found out the limit during that course instead experiencing it in real situation.
I sometimes ride nice sweeping twisties while I have my feet on my highway pegs, which I thought were high up the engine guards.... It is a wake up call when they hit, just like when my stock floor boards hit. It is nice to know the limits of this bike. I have not had anything else hit while leaning. It is not a crotch rocket for sure, but it can be a thrilling ride none of the less.
The Airflow boards on my CVO come with feelers. The feelers will touch before the board mounts and pipes (although I have scrapped both). I also have my boards spaced 1", and the feelers still do a good job.