why are all the spits and doms essentially the same volume except the 6'4", where the spit is 1L larger than the dom. What's up with that?

I was surfing a 6'4" Stealth (I'm 6'4" 190lbs and an intermediate surfer) I surf heavy, often messy, beach break at Ocean beach, San Francisco. Usually I'm only out in waves up to a max of 2' overhead.

I found it hard to get into waves on the Stealth, although I loved it once I was in a great wave. I sold it and got a 6'4" Spit, thinking it would get me into waves better. While it paddles WAY better than the stealth, and gets me in early, It feels too big. I love it in mushy stuff, but it's hard to duck dive and feels clumsy.

If I dropped down to a 6'2" Spit do you think that would be the ticket, or would I be back to having a harder time getting in?

How much is it volume vs rocker?

Thanks