Slitherine

Just going through three different books on tanks and their guns and it occured to me that the Cromwells AT should be slightly better than the Shermans and their HE slightly lower. Also noted that the Archer doesn't have the same AT as the Firefly? Just curious, not asking that everything get changed but I am curious as too the manner of coming up with the data, in general terms. Coupled with that would be the Cromwells armour, which originally was the same (slightly better) than the Sherman (76mm for the Cromwell, 75 for the Sherman on the Turret) but without the slope which should give the Sherman a slight advantage until the Aplique armour came out for the Cromwell bumping it to a much higher 102mm of armour (still no slope but nearing 26 percent more armour than the original design.