Edit to my earlier comment. Didn't remember G400 was so big, but I guess it's different because your grip isn't as wide as the mouse, because of those spots for your thumb etc.
EC1-A could be still good for you. I liked my G400 in terms of size and grip, but EC1-A's back had a weird shape or it was just too wide for me, so I switched back to my ZA11. But then again I have 18.5cm hands, so that's a bit smaller than yours. I would try EC1-A for palm grip if I were you.
EDIT: Plus my grip is kind of a hybrid. I grip my mice with my fingers, but not just with tips, but with whole finger, and palm isn't touching the mouse. So it's a relaxed finger tip or something like that.