Hello there!
Yes the 2-1 nap transition is confusing and I have found every child goes through it differently. My son, who is now 2.5, started refusing his second nap...his first nap was pretty set about 3 hours after wake-up time but at about 14 months, he went 3 days with no afternoon nap. So he then went to bed earlier. But on day 4, wham, he started napping again in the p.m and continued that until he was 16 months old. Then one morning, he started waking up later in the a.m, which of course pushed his schedule back and we tried one nap--worked well for a few weeks but then reverted back to an early wake-up and we went back to 2 naps again.
SO, he waffled back and forth for a good 2-3 months until we fully transitioned him to one nap at 18 months. He has always had tendancies for larking and so would nap early (10:00/11:00) and then for only 1.5 hours but as his body slowly adjusted to one nap, his nap slowly lengthened and moved closer to noon/1pm...it does take time, especially if your child is prone to getting overtired and waking early...
I have plenty of friends whose babies stopped napping in the a.m. so that was their clue it was time to go to one nap, other friends whose babies started taking mongo morning naps, etc. Best you can do is go with the flow and read your child's cues as much as possible!
HTH