wrote in message
oups.com...
Yup.
Many glass artisans do it routinely. Glass kilns with top elements are
unsuitable for stack firing because the top elements cause the highest
layer to be warmer than all other layers. Ceramic kilns with side
elements only will distribute the heat evenly and permit multi-level
firings. Here's a glass artist that uses a tall ceramic kiln to fire
as many as 6 layers at a time.
http://www.thegardengallery.ca/

Some glass kilns, with both top and side elements, permit the top
elements to be turned down or turned off to permit stack firing.

Keep in mind, when doing stack firings, there may be HUGE difference in
temperatures both from top to bottom of the kiln, but also from edge to
center.
Makes "some" difference as to element placement, but the biggie is that
heat rises.
Once you learn how YOUR kiln works, then you will be able to answer your own
question better than anyone here can.

Sometimes it is not a matter if something can be done, but is it efficient
and productive to turning out the creation that you want. When I want that
special bowl or sink to come out just right, I don't want to have to worry
about how the drawer pulls are doing on the next shelf down.