The base of the ball seems intuitively right to me too, but I think the edge of the ball is really as easy to see as the base, maybe easier when there's no line. With no line you have to sight from diamond to diamond looking down at the top of the cue ball, which makes it a lot like trying to "see" 1/4 ball.
An interesting wrinkle with the base of the ball rule: the line itself is outside the kitchen, so an OB can be sitting on the line and be OK to hit, and the CB must be sitting (at least slightly) behind the line - for breaks too.
About 20 years ago at South Bay Billiards in LA, I saw Mark Tadd and another player having a hilarious pantomime argument about this: Mark carefully puts the CB right on the line to break, the other guy leaps out of his seat, grabs the CB and slams it down 1/8" further back, Mark calmly waits for him to get back to his seat and carefully places the CB back onto the line - rinse/repeat. This went on for about 5 minutes - Mark got so far into the guy's head I think he's still there.
pj
chgo