Isn't there an option in the game menu (when you click on the map) to do that. I seem to recall someone asking the same question and I think you can tinker with that parameter somehow.

There is an option to do a manual cleanup, but I think that's different than the one that automatically happens every so often (the one where the little black box pops up saying the average FPS, Civ percentage, etc. and that all the corpses and damaged vehicles have been deleted). If there is an option to adjust it, i just haven't found it yet. I have been searching through the code to try and locate the line(s) that make that happen.

Hey! WotP is monitorising your FPS and seeing your PC is in bad shape, so it proceeds with that kind of thing. Check your settings under "Game Options" and low the spawn distance or other parameters