In this area of study, the devil is in the details, even more so than usual.
J and P share similarities on the one hand, while E and D share some similarities of their own, often because J and P are Judaic (southern) works, while E and D (possibly) are of Israelite (northern) origin, or influence. Obviously there are overlapping instances which can't be explained by this, but this is very important to keep in mind. Sometimes, we can corroborate this by comparing instances of usage in prophets that are known to be of northern or southern origin.
As to the Sinai/Horeb dichotomy, I think it's Kugel (although I'm sure this is not originally his insight) who puts forth the possibility that the different names stem from two rather different sites, that were fused into one during the process of tribal unification (there are other examples of this), building on the north/south difference.
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