Just changing all of the formations to surround is enough to increase encounter numbers, there is no need to adjust the numbers. But I'm not sure if it will effect some of the encounters actually appearing or not. I ran around the San Francisco area for ages and couldn't any random encounters.
But around the EPA there were plenty of Alien / Centaur encounters, also merchants with the surround formations are almost double their normal sizes.
But around the EPA there were plenty of Alien / Centaur encounters, also merchants with the surround formations are almost double their normal sizes.