Terseus

Yes, the info of your link is correct and correspond with the current source code, the best power efficiency is at 128 blocks above bedrock, this provides a maximum of 20% power efficiency gain. Too bad well, I'm not gonna change my drill placements now anyway. Edit: Link to the relevant source code line

It's from IndustrialCraft2, one of the latest versions I think. Here you have a video that briefly explains how it works: Unfortunately IC2 looks abandoned, in their Jenkins site we can see that there was only three builds in 2014.

Checked the source code and looks like the height doesn't matter at all, only that it can access bedrock. I have them at Y=10

I would ban sacred rubber tree sapling, those enormous trees probably generate a lot of lag: Edit: BTW, you may want take a look at the >banned items in other servers.