If you have a smaller crockpot, reduce the number of chicken breasts and cans of soup used. For larger crockpots increase same. I usually just increase the soups to fill the crockpot. Depending on how you're serving, you can usually estimate the number of people the dish will serve by the number of chicken breast. 1/2 to a full breast per person. I usually go 1/2 as the dish is rich and filling, especially when served over noodles or biscuits.
SIDE NOTE: I've tried this using fat free soups and it's ok; however, don't skimp on the sour cream. Low fat or fat free sour cream did not do well in this dish.