I have 2 separate cards and 2 separate credit lines. Did you say they're splitting your credit line evenly between the two cards?
It's always been my understanding that Sterling gives an auto CLI on a 9 month interval (unless you go into a store and ask for an increase for a purchase). At least that's what I was told some time ago by a customer service rep over the phone.
Both these Storefront brands and their financing dept are owned by Signet/Sterling Brands.....