I don't think volume helps --- unless it's all in the nose, like the Hover 160

It does help for getting up and getting a power stroke in when underpowered. Then it becomes a burden.
Even the LF Foil Fish, which is IIRC 17L volume, has more than enough to roll up a sodden S3 21 and plop it on top for a swim in. More volume just means the buggers charge downwind like a rocket when you've fallen off, too.
Big fat feet. With a single front strap, I tuck only my toes under for a start then assume a regular stance --- nice and open --- and if I bail, my foot slips out easily. Three straps, I have to jam my feet further in there. My SS board has even "smaller" straps

Three straps also forces my heel closer to the edge and I don't like the loss of toe input in pitch control. I tend to prefer not switching feet and just gybe around on my "good" side :D