Depends on the antenna, really. If you're doing all that monitoring on the stock ducky antenna for that scanner you're doing well.
Trees, buildings, houses, all of it contributes to how much you hear but nothing matters more than the antenna you use and how high that antenna is off the ground.
On the stock ducky from inside my home in Portsmouth, VA, I can pick up the Yorktown Naval Weapons Station which is maybe 65 miles line of sight from where I'm sitting, so that's pretty good for me. If I had an outdoor antenna (and someday I will) I'll more than likely hear a lot more than I am right now.
Sounds like you're doing fine, but if you can get an outdoor antenna mounted high up on your roof or possibly out a second floor window, it's like an entirely new world of stuff to pick up.
Good luck,
Paul