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

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.

All in your head.

When a mob first gets into melee range, it bashes. After that you have, I believe, 8 seconds (for an unslowed mob) before it can bash again, which is why your second spell has time to cast without worry of an interrupt.

Thank you!! so it's NOT all in my head after all!!!!

No it's still all in your head. The chance for it to land that bash isn't any higher