For me the squirt is accompanied by (and probably results from) muscle spasms, which only come with my stronger orgasms. The ejaculation zone, as you put it, is nearly impossible for me to get into any other way because if I try to do it alongside lesser orgasmic releases, I never can... It just feels odd building up to it that way, and I still have some control at that stage, so that last little piece of the puzzle holds me back.