When hammering on the top, are you using another on the back? Mounted in the vice?
No, just put the knife on the flat section of the vise (It's like a built in anvil section) and start peening the top with the modified punch. It does flatten the peen a little on the pins on the bottom, but still keeps most of the rounded peen. On the very top picture I posted, you can see what the bottom peen of the pins look like.