Sunshine-Supernova, Are you finding that you're not making stamp-contact in the middle part of the cookie most of the time? If so, it's quite likely that your topcoat is not level, but that's typical. The icing always tends to dip a little in the middle of a cookie as it dries, unless you dry the icing in a dehydrator.
That said, I tend to push down extra hard on the stamp (harder than you would think), especially in the middle of the cookie to make sure the stamp makes contact with the icing there. But be sure your icing is dry all the way through before you do this!
Please let me know if this solves your problem.