Have you considered solving the problem radically – by allowing hit-and-run tactics? You complain that it's difficult to play as mages, and yet you reduce their powerful spells. In Chaos rules, hit-and-run is allowed, and this is taken into account in the game strategy. For example, players try not to stay overnight near an opponent's castle without protection. If you really want to prohibit it, you should choose the simplest, clearest, and most unambiguous interpretation. For example, "cast any spell – you can't run away." Or "cast a combat spell – you can't run away." Quibbling about direct and indirect damage only distracts from the game itself.