Welcome aboard!! If you look at the main page of the forums you'll see a link to the pit master secrets podcast and this was a recent topic. I've seen the FB mounted high on some commercial smokers and some mounted low. My personal thoughts are that if I was going to use tuning plates I would mount the FB as low as possible. However if I wasn't going to use tuning plates I would mount it higher up on the cook chamber and have a deflector that sends the heat up towards the top of the CC, similar to a jambo. Don't forget the grease dam if you decide to mount it low. It also helps to run your numbers through the calculator and make sure everything is properly sized.
That’s the issue I’ve been running into geldings calculations seem to be off , and couple of the other calculators I’m haveing an issue w , I have the center line marked out and running out of time and money on this build tuning plates probably won’t happen