When I demo’ed the Azure, it first came in with ear hooks. My audie used a “flex tube” with a tulip dome on the end connected to the ear hook until the open fit conversion kit came in. In the standard configuration, you’d normally attach a regular mold and tube setup to the ear hook, an yes, it’s just a regular BTE like that.
But I think the original question is what is it about ear hooks and molds that allows you to boost the device’s fitting range 10 or more dB. My guess is that it relates to feedback control, and a regular earhook, tubing, and mold would be much less susceptible to feedback, so you can boost the power a bit.
With my Pulse’s, which are strictly open fit aids, I’m using a tulip dome for feedback control, so my audie tells me, instead of the regular open domes.