So I have 2 red dot equipped pistol, a p320 FS RX, and a P226 Legion SAO RX.

I understand the sigs are configured to be Combat Sight Picture(CSP). but is the red dot to be shot the same CSP?

Do I run the RX dot center of the fsp or when running the red dot I learn to aim above the irons and have it float on top of them

Keep the red dot off the iron sights. Use one or the other.

^ Agreed.

Focus on target (not sights), Put the thing on the thing, trigger press, repeat.
To give your brain a charge, keep both eyes open, put the red dot on target, then, keeping both eyes open, have a friend put a finger tip or lens cover up to completely occlude the front-site-side of the red dot lens. Eh voila, you still see red dot on target!
Brains are cool.

Sorta but not really. It doesn't matter where in the window the dot is, that's where the bullet goes (assuming he's zeroed the dot). The dot can be right on the irons or not, it makes no difference.

Ops - zero your irons, then zero the dot separately. They are two separate systems that compliment each other, but they do not need to be aligned together for aiming. IF they are both zeroed to the same POI, obviously the dot will be superimposed right on the irons when the irons are aligned to your eye. But you don't have to shoot it that way.

And yes, as quantsuff said above, focus on the target not the sights.
However, an occluded sight picture as you describe does result in a different POI than looking through the optic, and the difference is not consistent, it changes with position of your head, where your eyes are focused, and other factors.

Both eyes open. And practice the shit out of finding the dot during draws, the biggest problem with dot shooting in competition is finding the dot. Dry fire practice helps a ton. Make sure you practice two handed draw, strong and weak hand as well.