Clapton is known for using the middle pickup alone to achieve his famous woman tone. Don’t wanna sound authoritative here, please don’t get me wrong, but I’m almost 100% sure it was position 2 in the original recording and pretty much every time he played it with a strat. In the early years he’d switch to position 5 for the solos sometimes though. Regarding the Pensa era I think the original MK1 didn’t have coil splitting for the bridge so that would explain him avoiding position 2.