The distant AT Guns wish to skeedaddle....

[Blackcloud6]

I don't think the rule needs changing.  If the guns are set up well by the crews, they could be pushed back into the woods or among the buildings to cover their limber.  And yes, I know some guns are too big but many are not.  This simply could be a design-for-effect rule leading towards the more common, in the game, smaller guns.   Also "spotting" may not necessarily mean you see the actual gun, but you have observed the muzzle flash and dust, etc. and thus fire on the suspected position.