Hi Brian, yeah I understand the scope height "issue" for shorter ranges as I have a 50mm scope on a TX200HC - sometimes better at short ranges peering over the scope and aiming that way
I think a lot of people struggle with the basic idea of gravity having the same effect if you shoot up or down & hence instinctively hold-over when they aim a gun "up" at a target.
That video does a decent job of explaining it in nice sketches. There's also a similar video dealing with mil-dots which the same guy does, again decent stuff in terms of understanding the basics.
I'm surprised that this affects competition HT/HFT airgun shooters though? Sites which have +/- 30 degree and 30 yard+ targets must be few & far between?