In a way I guess that's right. Area, especially width at the SSR is what is needed. Since the velocity over the SS is so high, flow separates and the effective area at the throat is what gets cut off. Interestingly enough, every time I try to make the throat larger, flow goes down. This particular head has 50 degree seats and 88.5% throat. Conventional wisdom says a 90-92% throat would flow more. I have not yet been able to make that work.