I have read different to this in a Chiang Mai group - the method of reporting resets too if you re-enter so fist 90 day after entering always has to be in person. A couple of provisos here 1) Chiang MaI dos have some peculiarities in their immigration office 2) When I have completed my 90 day I always did it in in person it at Jomtien as it is efficient and there is a good pie shop nearby :-)
As you are in USA and have time I would apply there in your home country. Visas from neighbouring countries have recently come under a little more scrutiny by some Immigration Officers.
I saw a rejection that said foreign accounts are fine but they wanted certain documentation. Chiang Mai seem to be more particular in the case of extensions, not DTV, than other offices such as Jomtien. An agent told me they wanted a bank in Chiang Mai. I could use my Bangkok or Pattaya accounts but the documentation would have to come from the holding branch directly and not from a branch in CM.
I can see neighbouring countries getting more difficult. Immigration seem to have their tails in the air about it. There is politics at play. Anutin has been leading raids on short term rentals. Some of the properties raided are interesting but that is all I am posting here