Do you have the little tool that shows the proper shape the wheel should be.
I believe it's a combination of the wrong profile on the wheel, and you are going too deep. When you grind there should be no straight line on the side plate, only a curve. Your files should fit as closely as possible into that curve for ease of filing in the field. If there is a straight line from anywhere below where the file would rest and down into the gullet, that will be fine, but then you won't have a shelf to rest your file onto and you will either need to hold your file up manually or use a tool such as the husky roller guide.
Just because the factory can grind the gullet that low, doesn't mean you will be able to. When a chain is new getting the gullet is many times a second part of the process when grinding/ filling depending on the type of chain and the wheel/file size.
Hope this helps.