However you use the knife, the bevel pushes the waste away, and the flat side stays against the cut you want, exactly as you said. If you do it the opposite way, the bevel will tend to 'scoop' in the cut and you won't have a flat plane. I suspect that you and I make the scion cuts differently. If you watch the short video at the end of the grafting post at the blog you can watch me make understock and scion cuts.
A grafting knife is a grafting knife? Is a bonsai grafting knife different? Am I missing something here? Besides the price.
A Friend in bonsai