Yeah, it can get tricky about Amphur Muang, my address is Tambon Thapon, Amphur Muang, Petchabun. It covers quite a lot of area and Baans (Tambons). Petchabun is the Province but there are different Changwats ie Lomsak. If my Baan came under Lomsak for example then I would be under the Amphur Muang of Lomsak.

If you say you just live in "Amphur Muang" it won't mean anything to anyone unless you say the name of your Tambon (or Baan). If you don't have a Tambon then you would have to say you live in Petchabun.

Like a lot of things here it can be confusing and addresses are the worst. I had a Thai explain me what Muang is and it is basically everythng outside of town.