Do you remember lying prone in grass and not having any idea what's going on around you or crouching behind and not being able to peek above it since changing your stance would expose your entire body?
What if there was a way to just stick your head up for a short peek?
In Metal Gear Solid 3 this is possible and I think it would work in ARMA.
In MGS3 while in the first-person view holding R2 and L2 would make you lean right and left -- and holding them both at the same time would make you "stand on your tiptoes" and if you were lying down it would make you stick your head up slightly as long as the buttons were pressed.
In ARMA3, what if holding lean left and lean right simultaneously (by default Q+E) made you do the same thing? Naturally this would be a separate command so players could bind it however they wanted but now you should have an idea of how it could work.
Basically when standing this would make you stretch up or "stand on your tiptoes" in order to peek over objects just higher than you are, while crouching it would make you straighten your back and raise your head as to peek over something and while prone it would make you raise the upper part of your body just enough to see above the grass and as soon as the button is released you would go back to your previous stance.
When lying in grass you currently have to get up into the crouching stance or adjust up twice to go into the crouching down stance in order to get any idea of what's going on around you. If I was in the same situation I would simply carefully stick my head up and I hope this can be a feature in the game's development.
Check out a Metal Gear Solid 3 gameplay video on Youtube to see it in action:
The player presses lean left, lean right then both which raises your view above grass level several times.