I laugh because this post is so straightforward and frank - but it's not wrong.
It would definitely be best practices to do that. The game will be better for it.
However, if it works out that you really need to play with eight (I do it all the time), then whatever adventure you run, just make sure to not-quite double all the monsters. When this would result in you having to run more than, my gut says, about six monsters, then not-quite double their HP and damage output instead, so you're not bogged down with too much to do.
(When I say, "not-quite double", I mean eyeball it between 1.5x and 2x, depending on what the encounter already looks like and how good your players are at teamwork and using their characters abilities, etc)