Haven't worn my Theodore since I got the 961 because it is need of refurbishing.
Both times (about six years apart in build date) I sent in head molds to get the most accurate fit I could.
If I recall correctly, he only has two 961-style molds, the standard one I have, and the bubble chin. So if your head is too large or too small, he would have to adjust the fit by using less or more foam than he typically would, whereas if you went with a standard shell, he could size you into the most accurate pro's mold he's got and use just enough foam.