Why are you so focused on this aspect?
Why would you NOT want to use the red dot indoors? Reflex sights are superior to irons in a combative role in every possible way.
Do you understand that the standard practice is to mount a red dot so that the irons are visible through it and then aim the irons through the red dot's glass?
This is how it's done:
Attachment 54317
All I need to do to use the iron sights is to lower my head about a 1/4 inch. I can see the front sight through the Aimpoint, like this:
Attachment 54318
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