My LO isn't spirited but we basically work to a set nap time of 12.30. That is when he goes down when he is at nursery and so we follow that. The exception would be if he wakes super early (before 6am, not uncommon) on a day he is at home I would try to get him down for 12 and let him sleep a little longer, because early wakings are almost always a result of OT for us. Bedtime is 7.30, or 7pm if he had an early start or a short nap.
His A time does vary. Thankfully I am finding that in recent months he will tend to nap well regardless of how long his A time has been, which is such a help. He definitely does better with a shorter A time before bed. I guess our 'best' A times would be 5.5hrs in the morning and 5hrs in the afternoon - but if he wakes at 5am on a nursery day, he really has no choice but to push through 7.5hrs until his nap!!