Sight alignment for indoor range

Hello - I am a newer shooter with a Ruger Mark III with the factory sights. When I shoot at 21 feet, my rear square sight is aligned horizontally with the center sight. How do I adjust for a 40 foot and 50 foot bullseye as far as alignment?

That's a tough one. It can be worked out using similar triangles. But, it could be tough to hold that sight picture consistently. If the sights are adjustable, it would be best to experiment and see what works for you, gun, and ammo.

Should I get a rear sight with dots? I painted the front sight bright green. Not sure if I should place the front sight lower inside the rear sight or keep them all even and just place the whole thing at 12:00 or 6:00.

Keep the sights aligned. Figure out where to hold. Dots help some people. Most target sights are black. I have marked my front sights to give me something for focus.

Did you color your rear sight or leave it black? When you say where to hold, you mean 6:00, middle or 12:00?

This is the hold I use indoors:
Note the Front Sight post is in focus and the rear sight is a little blurry and the target is blurry.
Outdoors I use center hold--the sights look the same but my point of aim is the center of the black.
I don't find any advantage to painting dots on my sights.  I think the black gives me the most contrast against the target.
Welcome to the sport!  Have fun!

Thanks so much for your advice