It's sorta annoying the way that attacking forces can mass at the borders of a land control area with impunity, wait as long as they want to see if defenders will get bored and leave, then enter the area and get a first strike at the defenders due to the grace period.
My suggestion? Let people initiate combat with players who are in 75% gas from inside a controlled area using the rules for the gas level in the controlled area. Only apply this to land-control areas, like the longer grace period. And let our turrets shoot out into the 75% zone too
Simply and generally speaking there should be a way for defenders to 'do something' about people massing outside of their gas border, and the attackers shouldn't get a 'freebie' salvo at the defenders thanks to the grace time. This change will encourage attackers to try and stay inside the gas area or they will concede the first salvo to the defenders instead.