The thing is, the AT933/43 (AFAIK) is apparently supposed to be a lav mic when it was made (I could be wrong though). However, the AT853 is supposed to run via phantom power.
That is kinda backwards and wrong.
The AT933 is a phantom only, contractor exclusive series microphone line, known as Engineered Sound. There was no lavalier in this line. The line was updated to inclued a 943 lavalier microphone. It is identical to the 933, except that it has a groove for a lavalier clip.
The 853 series, known as UniPoint is a slighly larger consumer line, that also includeds options for battery or phantom power. It was recently updated with better RFI sheilding and slightly better statistics... This line does not have a lavalier...
Being electret microphones, their phantom requirements are relativly low, making them more versitle at 11v-52v....
The distortion issue is a matter of different capsule design IMO. They are just differnt mics....