Hmm...
My lo is up to more like 3.5-4 hours of "A" time at 8.5 mo...but that may be too much. However, when we try to put her down earlier, she does the 40 min nap thing all the time, or she fights her nap, which tells me she needs to be up later. We're still playing with it to figure out the "formula" for her at this point, so I wouldn't go by that number
Anything 1 hr. plus is usually considered "restorative"...but quantity of sleep doesn't necessarily mean quality sleep, which may be why you get a cranky baby. But that's beside the point...finding a magic "A" time number where your lo gets quality sleep even if it's a short nap is like finding a needle in a haystack.
It sounds to me like your lo is right on the edge of needing to increase "A" time. Try increasing 15 mins and see if that helps. I know that transition is hard. Some days they need that 3rd nap, some days they don't. When you get "A" time closer to three hours, you'll be able to throw out that 3rd nap completely.
Well, gotta go--sounds like my lo is still struggling with 40 min naps...I'll be darned if I can find the "A" time number for her at this point...guess I'll try 3.75 hrs and see if that helps. Maybe some other mom's can chime in?
*HUGS*
Sonya =P