In short:
Depends on mech, loadout and playstyle of said loadout.
In longer form:
Look up mech hitbox, it can make a difference on how you allocate. HBK for instance, if memory serves when looking at the right side torso(the hunch) even from the back side, most of it is considered front side torso. I put 4 points on the back of mine just so a laser grazing me doesnt show exposed internals from the back. I dont think i died once to a rear side torso on those mechs.
Awesomes: They eat it all in front CT, even when twisting sometimes. Stock they come with crazy rear armor. i put 12 points in the rear CT, and kept sides more even(not even, but like 70/30) because having weaker ST meant it encouraged enemy to maybe not aim for CT and also kept me from getting shot in the back and cored on my XL engined 9M etc.
Brawlers: almost all are heavy front load, with some getting revisions if I die to a back shot.
LRM boats. LOL back armor. If something gets you, you are too far from team or the match is lost anyway.
Fire support: very rare to get caught from behind, only mistakes on my part put me in that position. Spend enough time moving to flank and support it becomes silly to have more then basic protection on the back, based on mech.
Lights, and cicada: more balanced on CT, slightly more balanced on cicada ST rear, light mech rear ST depends on mech. Spider i find 80/20% is fine, I run 85/15 on the ecm one as I tend to hang by the team more and not run full speed all over like I do in 12 JJ 5v. Locust: doesnt matter what you do, your legs get blown off anyway.
really, all you need to do is start at a point you think might be reasonable for what the mech/loadout is, and then lower rear armor and frontload it slowly until you start getting cored from the rear, and then throw a point or two back on and call it good. it will vary by pilot, so each pilot needs to tweek that in.
*edit: I guess another way of saying it: if you ARE NOT frontloading armor, and die to back shots more then you like, you are either not paying attention, or runnig around like a tool during the match, running away far to much. Mechwarrior is not CoD, and the best method is to not get into a position where you need to run away in the first place, as most of the time the enemy has something faster then you, or enough range to kill you anyway. it is hard to run 1200M away from the enemy if you are in the wrong spot
When I spectate a 110kph mech trying to run away from a commando, all i can do is face palm. No amount of back armor will save you and allow an escape.
Also, there was a joke thread about taking an Atlas DDC and putting almost all armor on back and then walking backwards into battle( the idea was once something got in front you would blast it to bits anyway) but i dont know anyone that tried it, or at least recorded it for my entertainment.
Edited by Eldagore, 27 January 2014 - 08:23 PM.