You never want more armor on your rear than necessary to take a surprise shot, i.e. 10-20 is the maximum you want there on all mechs, I would tend to assign only 10 on all rear torsos (10-10-10). On a very slow front line brawler like an Atlas you can do 10-20-10 or 10-15-10, but thats already quite a lot.
Now why not more (e.g. people say they want to torso twist etc). Simple: Why would you assign armor to your rear only to create the need to show your rear to your opponent? If you think about it, there is absolutely no reason to do that. In TT some mechs had some minor armament on the rear (e.g. Archer with 2 MLs on the rear), but in MWO it is pointless to do that. So why is 10 points a good choice? Because that tends to be a common factor. It's an AC10s shot, 2xMLs or about a LL or a PPC. 10 just allows you to take one such surprise shot before your internals take damage. Taking more than 10 damage doesnt necessarily kill your mech, remember that even the engine can take 15 damage before it dies. As an example: If a Yen-Lo-Wang sneaks to your rear and get a AC20 round from point blank into your rear CT 10 points armor will be goen and 10 damage will enter to your internal - youre not gonna go down from that! Frankly with above named scheme I just cant remember the last time I died to a shot from the rear, it simply almost never happens.
You can lower your leg armor a bit, but I would always - no exception - strip armor from the torso or head. Also leg armor needs to be carefully evaluated how much you really want to strip. Remember that if your opponent finds out that a little fire almost critted you in the legs he might decide to continue working that way.
Edited by Autobot9000, 18 October 2013 - 05:21 AM.