The link Google found was in Thai language blog on tax issues, however dormant for nearly a year already. More specifically, it was the quite lengthy post with background information on the local tax in TAO. I tried Google Translate with the text, and while it is quite garbled the following section is the one which caught my eye
and now Ministry of Interior has proposed a draft Council formulate his district and Tambon Administrative Organization canceled by the new version. Abt. class size to the size of the roast will be divided into 3 size is large Abt. Abt. medium roast, a small town Abt. hold of the type of Abt. SmallAdding to that the first comment to this post, I understand it that way that with the 5th amendment of the TAO act the five levels have been reduced to three levels simply named "small", "medium" and "large". But my Thai is not enough to find any confirmation in the law text which can be found in the Royal Gazette.