I run an all melee group. What you describe is normal. What I have done to sort of mitigate this is to have every 5th button press in a "spam" rotation be an IWT. That way if they do run at least they will not get very far and attack the target as intended. IF they stand still at first this "spam" also gets them to attack. Basically I use IS and set up the keys to do dps,dps,dps,dps,iwt over and over. Works well.