The problem is we're having is that suppression should both keep units in place, and not do it. At the same time. How about this then; While suppressed the AP cost for fire is slightly increased, the accuracy is moderately decreased. The AP cost to move is slightly increased. If you move and then fire, that unit's turn ends. Moving and then firing costs all remaining AP. This would simulate popping out of cover to fire, which would immediately illicit a hail of bullets. This now occurs naturally in the opponents turn. (If they decide to shoot) Next turn, you can fire again, and move back into cover. Or just make a run for it, or whatever, but still suffering from higher AP costs.