I do alter the bell for trial and error, sometimes I will come across this situation where it is below the outer pipe causing problem to lift it up.
Bell shown in a position where you will have difficulties lifting it up
A simple way to lift it out is by using "sucker" that come with aquarium pumps or even cup holders. Just stick it on to the dome.
And lift it up.
I experiment a lot with bell length, one way of extending it is to use spacer, made up of the same pipe. Insert spacer first then the bell pipe. If bell pipe not holding in place due to it short length.
I will use RTV sealant, reason for using this sealant, is that its easily removed if I need to do more adjustment. If I use the PVC pipe glue,, then its a permanent fixture difficult to redo.