Hello Roger,
Without knowing the whole story, it is hard to gage where the rub is. The size of the panel could make a difference.
In general, specifications are generally designed to make certain that most product fits through the window and assume worst case scenarios. They might well be able to make the product to meet your requirements but don't want the be tied down to a tighter spec.
There are however manufacturing methods that can be employed that could make it work nearly spot on.
Can you use or have you considered use of a photoimagable coverlayer? This might solve some of your problem.
Good luck,
Joe