One thing which I remember from when e started dropping the nap was that when she was getting ot she needed a long nap to get back from it BUT (and this is the critical bit) it had to be a nap that she woke up from herself and bedtime had to stay the same. So when I could tell that she was getting ot, I would put her down for her nap at the usual time and leave her - once she slept for 3 hours and I spent the whole time fretting that she would never go to sleep at bedtime! - and I put her to bed at 6.30 as usual and she slept for 12 hours. We could only do this once in a while, though, not as a regular thing, but it did help to reset when things were going off the rails a bit. Perhaps it might be something to try once during the process to see if it can start you from a better place?
We capped the nap from very early on with both girls (for us it was more that they had to be awake by a certain time rather than they could only sleep for a certain amount) and this was really helpful with e when things were going off track.