Assuming you are American and playing w/ a fairly typical rule set of something like H17, DAS, DA2, LS then can give yourself probably .5% at TC2 and .5% per increase in TC afterwards. So full kelly would bet something like .35% at TC 2 and add .35% per TC. TC 3 .70% TC 4 1.05% etc. This would be full kelly, but if you want less variance you could bet some fraction of this amount. But these are rough approximations, you are much better off buying CVCX and then simulating your exact conditions than relying on any sort of crude rule of thumb. Especially if you ever play games with an atypical rule set and thus differing advantages at each true count. CVCX is especially valuable when you are comparing different counting opportunities. But also so you can have a good idea about how much risk you are exposing yourself to for how much reward and to understand the variance that you are looking at.