Do mobs hit you harder/more-often when they first approach you?

[Portasaurus]

Say you snare a green mob, and then while it is approaching you, you start to cast a spell on it. If the mob is within range before you finish casting the spell, it seems it almost ALWAYS lands a successful hit on that first strike (often stunning me and therefore interrupting my spell). Only AFTER this first successful hit does the mob start MISSING (and missing a lot) and then I can get my spell cast on the 2nd attempt while the mob is in-range for the entire duration of the cast.