Personal choice plays a big part here but when all’s said and done a shooter should be largely unaware of the rib if he?s focusing hard on the bird.
Assuming the gun is a correct fit the only time you will be vaguely aware of the top rib is when the stock is mounted, and the muzzles are swinging with the target.
This view of the rib in our peripheral vision is, according to some, the thing which makes one rib more ‘pointable’ than another.
I tend to prefer narrower ribs because they?re less obvious to the eye and therefore do not draw my concentration away from the target.
However, it should not be forgotten that an O/U?s top rib is ventilated to dissipate heat generated by fired cartridges from the barrel.
Wide ribs, theoretically, push this ?shimmer? further out to the sides to leave the sighting plane unaffected.
In other words there?s less chance of the shooter?s view of the target being compromised when the gun is shouldered.