@chows Your definitely right in assuming that the ratio of ingredients will have an affect on the texture and chew of the caramel. But there's many many ways of making caramels, they produce different results. Like @Chocolot mentioned, check out Peter Grewelings book Chocolates and Confections, thats a very good place to start, it gives reliable formulas and a good text on the role each ingredient plays. I'd also say pick up a copy of Fine Chocolates Gold, by JP Wybauw. His caramel formulas look different from Grewelings, but they work, and may be the texture your looking for.
I suppose what I'm saying is that all three of your caramel recipes are different, they all will come out differently. For the coffee caramel, I think its the recipe itself that is broken, it has nothing to do with the espresso powder. Its a bit easier to find a reliable formula for plain caramels in one of the books, then you can start flavoring that base recipe anyway you want, rather then trying to troubleshoot and adjust a recipe that was found online.
Edit: I wanted to add, go on Amazon and purchase a used copy of the 1st edition of Chocolates and Confections, it's easily the best $20 you can spend on a solid reference for candy.
