While it certainly is more comfortable shooting a thermal scope with a good check weld where it just comes up naturally and your check rests on the stock and you're looking dead-center of the ocular lens, there is a difference between shooting a normal day scope and a thermal scope.
With the day scope you are actually looking the the scope and magnifying an image that comes in through the Objective lens, so having that perfect check weld is critical and will result in better accuracy. If your eye moves the crosshair moves.
With a thermal however, you aren't actually looking through the scope. Rather, the thermal camera is reading the image through the objective lens and the camera's software projects the image onto the small screen we view through the ocular. In other words it is just a miniature TV screen. While I have noticed that the SY seems to give a sharper image if the eye is centered correctly looking through the ocular, I do not believe that you have to acquire a perfect check weld for accuracy with a thermal scope. As long as the crosshairs are on the acquired target, it won't make any difference where the eye is placed to look through the ocular to view that little TV screen.
Yes, the perfect check-weld is certainly more comfortable feeling on a thermal scope, and truly necessary for accuracy on a regular scope, but with the thermal you are only viewing the little TV screen so where you hold your eye may feel awkward but if your weapon is sighted-in correctly and the crosshairs are on the acquired target, you will hit the target.
It seems beyond any reasonable doubt that the newer and smaller thermals appear better suited for AR's, look better on them, and feel better when you bring them up to your eye.