I don't think there are really many characteristics out there that ACTUALLY fully describe ONLY J/P characteristics. However, I do think the J/P dichotomy is more or less 100% either way. Functionally, a J always extroverts judgment of some sort and introverts perception of some sort; likewise, a P always extroverts perception of some sort, and introverts judgment of some sort.
As a digression, I don't think a sliding scale is an acceptable way of looking at Myers Briggs simply because of the functional theory behind the dichotomies. Try to think instead of using various degrees of preference for different functions, of which everyone has four. Each Myers Briggs type has intuition, sensing, feeling, and thinking; the definitive characteristics lie in how much preference is given to each, and in what attitude the function lies (introverted or extroverted). As an example, ESTP's who give a high priority to feeling aren't just EStP's (barely T), they just give a higher than normal favoring of Fe in certain situations. They use all functions; the P and J simply determine the attitudes. So ESTP's would use Se --> Ti --> Fe --> Ni and ESTJ's would use Te --> Si --> Ne --> Fi. The functions are completely different with just one letter switched. So do you see how P and J can't really (theoretically and in most real cases) be close on a sliding scale?