You got Gap Generator to block Risen Railgun. Even if enemy uses Scout Raven + Risen Railgun, it's pretty where to know where exactly the Airfield is, especially when it's in the center of the shroud.
A player shouldn't have to do that just to block a cheap move, the Gap Generator is expensive and requires a lot of power, besides that, most bases tend to be spread out so a Gap Gen isn't going to cover the Barracks, War Factory & Airfield in most cases, which would require possibly 2 Gap Generators, and even more power.
If the enemy decides to use Scout Raven then it's pointless anyway. Railgun damage against Jets needs to be nerfed, no excuses.