[RPG] How to heavy-armor melee characters practically close in on ranged enemies

Retreat is for when you all need to run!

Fighting withdrawal is always better for disengaging from combat, if it will actually do the job. A withdrawal only works if the opponent is unable or unwilling to follow to maintain the combat engagement – if they do, you've wasted a turn failing to disengage.

The other purpose of a withdrawal is to back into a more favourable position – into a doorway or narrow hallway, for example. However, if that choke point is beyond ½ your movement, then you have a dilemma – a fighting withdrawal won't get you there in one turn. If time is of the essence, do you try to do it in two turns of withdrawal, or do you break engagement to flee to the superior position and risk a strike at your back?

The difference between them is always that, sometimes, those few feet of difference can be worth the risk. If they're not, then a Retreat action isn't worth considering.

And yes, the monster gets its attack. Turn order is merely a game convenience for play simplicity, and for representing a slight combat advantage, but really every attack (by creatures that survive the whole turn) are considered part of a simultaneous mêlèe. The retreat grants that extra attack – as GM you can roll it at the time of retreat, or on its initiative turn, and the difference is a matter if convenience rather than whether the target is still viable. Think of it as happening "sometime" during the turn when the retreating character exposed themself to danger by recklessly turning tail, but do the actual roll and damage whenever is most convenient.

It’s very difficult to prove a negative, but I am reasonably confident that no rule in 3.5 or Pathfinder explicitly states that all armors of a given weight class slow you down by the same amount. In 3.5, at least, there were certainly a few super-heavy armors that reduced the speed by more than your typical heavy armor (Races of Stone had a couple of these).

So yes, every Medium or Heavy armor must somehow explicitly state its own speed reduction, even if the overwhelming majority of them have the same speed reduction. On the other hand, if a given case failed to do so, I’d just chalk that up to the designers not realizing there was no such general rule, since it usually is so consistent and armors which slow people more or less than others in their category are quite rare. It’s also worth keeping in mind that it is consistently weight category that we should consider, not sheer weight.