here's the deal. larger than normal mains typically means either 1) an inefficient motor or 2) a friggin lot of airflow is being moved... since it's mostly stock, i'm going with option 1.
let me explain and I'm sure most of you know this; vacuum is what pulls the air through the main jet... with the larger main, that's telling me that your motor is not pulling a lot of vacuum, probably a little to due to the slightly higher elevation not getting as much air volume, and since it's not pulling efficient vacuum it's not sucknig a lot of fuel, so opening the main jet orifice allows more fuel to come through to compensate.
In truth, that bike running 370s is probably not using much more or any more fuel than FTW's banshee that runs 280s... it's just getting the fuel in a different manner. If your bike, Milo, was then ported, your jetting very likely could come down, due to the increase in airflow and vacuum. I would almost consider putting the stock reed cages back in with some Boyesens or something similar until you port your motor, see how that affects your jetting and performance. Seeing that the vacuum and efficiency is not there, I don't believe your motor is making all the power it could or should.
if it runs good, isn't lean and your happy with it, go with it. if you want to experiment a little, take my suggestion and see where it goes.