Welcome to the board. Finding fish is the most difficult part of this great sport. Granted, getting them to bite is a challenge. What I think you're asking is how to find bigger fish.
Fish, big or small use similar areas for feeding and they all have one thing in common, forage availability. If you just take this one fact into consideration (I don't recommend making decisions based solely on one factor), should the bigger fish have been there too? If you answered yes, then evidently they were either holding in the prime areas on that spot, they were not active, or they didn't want what you were offering.
If you answered possibly (good answer), the one thing you did incorrectly was to continue fishing for the 13in. fish. A wise man once said: "The definition of insanity is doing the same thing over and over and expecting different results."
If you answered no, then you need to ask yourself where and why. To be really successful at this sport you need to understand both the fish you're targeting and the forage they are feeding on. The fish's habits don't change, they are fairly simple creatures. Their movements and attitudes are, however, governed by many different factors. Something as simple as a change in diet from one form of forage to another ( ) or as complex as PH or O2 levels can leave us, as anglers, confused. The fish just react to their environment. Go figure