Apologies if someone has linked this before but this video seems to be one of the more helpful in terms of explaining shooting at vertical angles. It isn't intended for an airgun audience but its obviously still relevant.
It does have maths in it but easy-peasy stuff with nice diagrams.
A less useful video but it is an airgun and does demonstrate the effect at extreme angles - although I wish to god he'd hit the drone & it fell on him, would have been some laugh
Drone lunacy starts at about 6:30 if you want to skip the (not good) explanation section.
Oh and "hello", I should have posted in the intros forum first but I suck at forums these days - will get there....