I like my awl to pretty well match the prickmark if it is too small it will be easy to make your hole in either the top or bottom of the mark if you are not carefull, making your stitching look untidy.
My preference is a small mark & small stitches but that's just me its a personal thing everyone is different. I would give Dixons a call & see if they will make things right for you, as I said earlier in this post it's been a good few years since I dealt with them & things may have changed. I never saw how the tools were modified, they used to just take a stock item off into the workshop, a few minutes later they would return with a hot, modified tool which was then wrapped carefully in oiled brown paper, the guys there in those days were lovely.
I really hope they make things right for you.