The EOTech is designed to mount directly on the flat top and it will co-witness perfectly.
Risers are optional for sure. The split is easily 50/50 for those who want a true co-witness and those who want a lower 1/3 co-witness.
I like a true co-witness.  The 1 MOA red dot will display on the tip of your front iron sight. (almost as if it were illuminated). If your EOthingy dies, you don't have to move your head a adjust your cheekweld for a new sight picture. You just keep shooting with a non-illuminated front sight post.
Check this thread
The third pic down is a true co-witness. When you look through the iron sights, the dot is directly on the FSP. In the fourth picture down, the rear flip sight is folded down. The dot is no longer on the front sight post, but it would be if the camera had a proper cheekweld
As you can see, it is a much cleaner sight picture without having to use a riser.

I only like a riser if a fixed rear BUIS is used.  That said, I don't use either.