Is this for PvP or PvE? I am strictly PvE and I manually control my IWT, so I very rarely get runaways. If you want to keep it built in to you spam key, you may want to try either spamming slower or making sure it doesn't got off with every single press, or setting up a toggle that turns off the Click-to-move part. Of course, turning off click to move means they won't run up to chase something, so you'd only want to do that if you are going to be staying in one spot to fight. Either way, spamming too much is usually the main cause for the running off. Reducing the frequencey with which IWT is spammed one way or another should help.

As far as ranged vs melee, I have IWT set with 1 keybind for everyone. This is the one I use for questgivers, flight paths and things like that. But I also use it for getting back into range or refacing in the case of fearbombs or the like in combat. Melee has an additional keybind, which is the one that I spam for combat.