I know there's settings for suspending in logind.conf and also in dconf, but no idea what controls what happens when you close the lid and do nothing, I use my old laptop exclusively through a screen sharing program that keeps the screen off, and it works fine, so it might actually be the graphics driver.

If it's just the CPU scheduler being changed, you could always figure out a way to run your own command when the lid closes, to revert the changes to the way you like it a few seconds after the lid closes.

https://askubuntu.com/a/1140362