The book I often refer to written by a sleep expert with children with over 30 years experience, says the morning nap develops first as their brain is developing and the afternoon one comes later. It's quite interesting. He doesn't mean don't put them down for naps in the afternoon, he just means they sleep longer in the morning nap, and then the morning nap falls away as they get bigger and then a long afternoon one develops. His book: www.amazon.co.uk/Healthy-Sleep-Habits-Happy-Child/dp/009190255X/ref=sr_1_1?ie=UTF8&s=books&qid=12655 35943&sr=8-1
I personally wouldn't limit the morning nap The Boosh not at 6 months old. And put them down for their second nap when they seem tired instead (if they slept a long time in the morning), i.e. rubbing nose, eyes, yawning, going quiet etc. lay them down when you see some of these signs. Make your own routine almost? If the gap between naps is too close they may not settle for the second nap at lunch, if you see what I mean, so it maybe better to make your own routine for now, until your baby is slightly older and changes again
Once they're overtired they can get very distressed and then not actually settle for a nap, even though they're tired, or not sleep very long, so it's always a tricky balance on meeting their needs at this age. At least I've always found this with my two. And they can be so exhausted at night if they don't get their decent naps in the day, that they do exactly what your little boy did and will not wake for their feed at 10pm. I suppose some parents may keep their babies awake in the day so they sleep better at night, but my little ones got distraught without their naps, so that never felt right to me...
Anyway I'm no expert, I've just read a lot of books and learnt a lot the hard way with my 2 kids.
Hope things are getting better now x