I think sugar content has lots more to do with geysers/ not geysers than fill level. Lessee, you want to card by 2-3 volumes of CO2, an inch of neck +/- would be 5% more or less gas in the beer instead of in the neck?
I've always filled to within an inch, per Papazian. I hate bartenders that don't give you a full glass. I bought the big diameter bottling wand, it's faster. It would leave the whole neck empty if I didn't top off by touching the wand to the inside of the neck.
So far, I've had more experience thinking than I've had brewing....you don't think they are mutually exclusive, do you?
72 batches so far,
48 wine, mostly Loquat, peach, plum, prickly pear
23 beers and ciders
1 Tequila, from a prickly pear wine experiment that didn't work. I call it "Prickly Heat"