Last year I planted in Christmas week one row with the top of the clove about two inches from the surface, one about 1" and another quite shallow. There was no discernible difference in the results - they were all small :D
I've already planted this season's first batch but we have light soil so, following the reasoning above, I'll do some at four inches and some at one inch in both the next batch and the spring planting to get a comparative.
Actually I suspect it mostly depends on the weather pattern and there's not much you can do about that.