30 is probably unnecessary low.
If you have a Pro Stick Plus, try 38 in your location.
Basically you want to turn up the gain as high as you can without losing aircraft when they are flying low and close to your antenna.
Think of the gain as volume and the receiver can’t understand something that is too loud.
But if it is too quiet the receiver can’t understand it either.
Of course you only have one volume control for all the aircraft, which can be very far away and very close.
So it’s almost always a compromise.
(The antenna “hears” better towards the horizon than 30 degrees or up. So if a plane passes at more than 20000 ft it is either far enough away or at a weaker receiving angle of the antenna, so it never overloads the receiver. But if the plane is flying at 5000 ft or lower, it is much easier for it to be too loud to be heard.
Also don’t worry about the receiver, it can “hear” perfectly fine as soon as the strong signal is over. So it can still hear the other airplanes)
If you want some more reading on the topic: Thoughts on optimizing gain