Something I think a lot of people fail to think about is that combat isn't a series of specific actions that start and stop on a player initiative or specific phase. That's just how your allowed amount of actions is measured.
To give an example, in RMSS, if you move cast Bladeturn in Snap, move 20% in Normal, and attack in Deliberate. You didn't stand still casting a spell, then suddenly shoot over to the foe, come to a stop, then perform your swing like wooden toy. You cast Bladeturn as you moved towards the foe, making your attack (or series of feints, thrusts, etc) as you approached.
So 'going around' someone in melee shouldn't really be a matter of "But I have enough movement to do that!" Always assume everyone involved in melee is continually moving. This is why we assume two foes never get a flank on you. Because the three of you are constantly moving and the person getting double-teamed is going to constantly keep the two foes on his forward flanks. No, this isn't FULLY realistic, but melee will NEVER be fully realistic. So some common sense rules need to be put in place that, unless given a very wide birth (i.e. the person would have to disengage melee in order to block you), you should be able to 'block' people. All the people involved just need to remember melee combatants aren't static. You don't just stand there taking turns swinging at each other.
This not the issue, as a GM if I was to use the same tactics when outnumbering the players someone would be killed, a squishy at the back or whatever.
I realize you're trying to avoid being too deadly, but in the end I think your players will either need to position themselves better, learn they can't win every fight, or suffer the conditions any intelligent foe would create.