Playing devils advocate here, but the precedent is from a long time ago when there were only 319’s and 321’s on property, and there were two different pay scales. With only a couple 321’s flying out of certain bases, only a few pilots were enjoying the higher paying fleet. Since you can’t bid for it, the override was a way for all pilots to get a taste, rather than a few who do all the 321 routes. The contract language is a ratio of the total hours flown by 321 to 320/319, if you further dilute that ratio with hours flown by the 220 as well, ain’t going to be much of an override left.