This may depend somewhat on your intended use. In LE I always preferred to have the back-up irons in the lower portion of my Aimpoint T-1 when I utilized them. In this manner when covering/targeting a bad guy, with the red dot placed center mass, or in the cranium area for a high-percentage shot, the sights normally did not obscure my view of his hands/area of his waist.

If you have absolute co-witness, the front sight, rear sight, and red dot afford you less of an open view of the perp.

As an aside, I run a fold down front sight on my work carbine and prefer to view only the red dot. The front sight/rear sight/red dot field of view always seemed too "busy" for me.

This works for me. YMMV.

JPJ

P.S. With the Aimpoint family of red dot sights, parallax is a non-issue. Put the dot on the target, press the trigger to the rear, repeat as necessary.