XS Big Dot Sight Install

[zrockstar]

Hey guys, I am installing some SX Big Dots on my Sig P239. First question I have, is do I want to center the rear sight in the dovetail or on the frame or on the firing pin (which seems to be the center of the frame as well)? When I have the sights centered on the frame or firing pin, they are not centered in the channel, so which one to go with? Also once I apply the red thread locker, how easy is it to make small adjustments to get windage correct? Thanks.