Why don't you make Veigar's ult explosion size scale with his AP too?
Seeing a gigantic ball of blue death hit something and make small fart particles is very anticlimactic, so making the explosion larger as well would make it look cooler, no? (purely visual change)
Here's a video showing his ult's explosion size in various ways.
https://www.youtube.com/watch?v=p21QUpiT1B8
And here. https://www.youtube.com/watch?v=93LPokcZ_is Like seriously, the explosion on the tristana looks so damn small compared to the projectile.