My understanding is that avoidance does not depend on position. Certainly Jedi player characters happily deflect blaster shots from behind. If reduced avoidance from behind could be documented, it would be very interesting. I will try to test next time I'm at the dummy.
On the other hand, today I witnessed what seemed to be a dramatic difference in parses due to lag. I was testing in a high-population instance of Republic Fleet (~250 players), and getting consistently low numbers in half a dozen 5-10 minute parses. I couldn't figure out why my numbers were so low. I then switched to another instance that only had 10 people, and with no other changes to gear, buffs, or rotation, my DPS went up by over 100 points (from high 1500's to 1700). I attribute this to lag, since while on the high-pop instance, my abilities were noticeably hitching or being delayed.
Shouldn't affect comparing two relics one after another, but for tests spread hours or days apart, the server conditions may be more important than any gear...
You just had to mention server lag... I did one parse with the BM relic, did about 1600 EDPS (I got a few upgrades + 2 more augments + Nightmare Pilgrim buff) and when i went to parse with the Proc relic the server lag made in unplayable... I'll try again later in the week.