The advice above is all good,but just a couple of thoughts.
Butts are the most forgiving/least stressful thing you can cook.
You can put your largest butts on the warmer top shelf,to balance cooking times.
Yes ,the direct heat from the cook element can harden up the area next to it ,a little bit.
As far as shaping a butt,some may trim to flatten ,to get on a shelf-it will shrink.
Some may stand on it to flatten it.
Some will butterfly/make boneless,to give more surface to take on smoke and develop bark.
Some will leave it loose,or even cut some slash marks to get more bark/crispy areas.
If it is larger,8 lbs +,some may spray with apple juice-some won't.
Don't get too technical,just learn how to cook the butt, and when to pull it off the heat.
Just a couple of thoughts.