Re: APS-2 what fretboard radius is it for?
From what you are describing, I'd say to use the flat poled APS-2 for the Warmoth compound radius.
What I notice about the diff in tone is that the raised and staggered vintage style poles (as in the APS-1 or SSL-1) have a slightly brighter, glassier and more vintage tone because the poles, especially the middle poles, will be closer to the underside of the strings and the bobbins will be further away and that, IMO, results in a brighter tone.
It seems to me that single coil pickups with flat poles sound just a little warmer and more midrangey...perhaps because the flat poles allow for the entire pickup, including the bobbin itself, to be moved closer to the strings.
Lew