Hi Pochahontas,
My LO (who's a few days shy of 7 months - also spirited/textbook) is doing the same thing. He used to go down easily at exactly 2 hours and sleep for 1.5-2 hours. At 6 months, I started having difficulty putting him down for naps and whenever I did, they would be anywhere from 30-45 mins max. After a couple weeks of tweaking, I found his perfect A time to be 2hrs20 mins and 2nd A time to be 2hrs30mins. I had to take him for a walk for his last 30 min catnap (A time anywhere from 2.5 hrs to 3 hours). His naps/sleep changed as well to 1hr10mins in the morning, 1.5-2hrs in the afternoon, and he went from sleeping 10.5hrs/night to 11.5 hrs/night.
2 days ago he started being really difficult to put down again, even though he seems tired and starts to fuss. He also started skipping his last catnap so I put him to bed earlier - thank goodness for daylight savings time!!! Anyhow, it looks like it may be time to tweak again - maybe your LO needs longer A time too?
I just put him down for his first nap with A time of 3 hours (I tried at 2hrs20mins but he woke up after I put him down so I got him back up and played quietly with him until he started fussing again). Had to use a soother to get him to sleep though (which I weaned at 5 months) so 3 hours may have been too long... good luck with your LO!