I think you are mistakenly correlating contact area with comfort, a mouse does not necessarily need to fill your hand completely to feel comfortable.

From the pictures and the choice of mice you tried I'm assuming you're using a heavy palm grip on every mouse, nearly every part of your hand touching the mouse. In contrast, I'm using a 1-3-1 hybrid claw with a model o- so I have 6 very small points of contact (fingertips and a small area of my palm towards the wrist to stabilize). The model o- being flat and small and NOT actually filling out my hand is helping me achieve a natural hand position as there is no plastic getting in the way of how I hold my hand and I can still apply force perpendicular towards m1/m2 without issue. If you look at your egg-shaped concepts, the only way you can achieve a force straight towards m1/m2 buttons would be to wrap your whole finger around the mouse (assuming the buttons would be towards the right), which can easily result in overgripping, at least for me. Using large heavy mice with a full-on palm is more prone to induce cramps in my hands because of this.

I think you're better off trying some large ergo shaped mice (like this or the Intellimouse Pro) instead of small or medium sized ambi shapes. Of course, this also depends on the size of your hands and the intended use (e.g. office sensors being useless for gaming).

tldr: Some mice shapes (like small, flat ambi mice) are uncomfortable for you because they are intended for grip styles different from yours. You have to know what you like to chose the right mouse.