My LO is just over 14 months and I've been aiming for set naps for a couple of weeks now and I do find they are working pretty well. He even slept though the night for the very first time last night! Maybe that was just a coincidence though :-)
I don't have that much of a variation in get up time though. He gets up between 6 and 6.30am most days and we do nap at 11.30 give or take 10/ 15 mins. He does often wake up at 5am but he doesn't get out of bed until 6am at the earliest so even on those days - I stick to 11.20 nap at the earliest.
I have found that the set naps have taken the guess work and therefore the stress out of the day - so I'm much preferring this way at the moment