This is what I do to get my 901 atomizer to seat properly.
Roll a strip and insert into empty cart. Then, using a pair of tweezers, pull the center of the roll back up out of the cart and trim off approx 1/4 of an inch from the protruding coils.
Push the roll all the way back down into the cart. The center should now be recessed to leave room for your atty. If it doesn't sit quite right the first time, you can pull the center coils back out and trim until it does. You can also spread the center of the roll with tweezers and loosen or tighten the roll as needed so that it doesn't stick on your atty.
Roll a strip and insert into empty cart. Then, using a pair of tweezers, pull the center of the roll back up out of the cart and trim off approx 1/4 of an inch from the protruding coils.

Push the roll all the way back down into the cart. The center should now be recessed to leave room for your atty. If it doesn't sit quite right the first time, you can pull the center coils back out and trim until it does. You can also spread the center of the roll with tweezers and loosen or tighten the roll as needed so that it doesn't stick on your atty.