A Quick Look at Heat in the Kiln
Heating elements do not create small amounts of heat by trickling the electricity through to create a small amount of heat. To make a small amount of heat the elements turn on completely but for a short burst of time. Those little heat bombs then disperse into the kiln. That means, no matter how you program your kiln there will be moments that the air close to the elements is a lot hotter than what your controller reports.
If there is a piece of glass close to the elements it is going to take these burst head on.
This is one of the reasons that lid elements are preferred when firing glass: the edge of your glass may be closer to the side of the kiln – but it is exactly the same distance from the lid as the center of your glass.
Will uneven heating in your kiln break your glass? To answer that question you need to understand what characteristics of glass put it at increased risk.