I have an old pair of tin snips that I have got very sharp on the Tormek, but these seems to be an issue that they cut great down by the tips, but as the material moves closer to the pivot point, it cuts less and less...
It this an issue with the sharpening or more likely are the blades bent and just not meshing properly? (the photo is an example of what they look like... not the actual tool...)
I have those same ones and I would try the scissors jig (SVX-150).
Perhaps they are not tight enough to engage properly near the pivot point. Is the pivot pin adjustable? I looked online for some info and found a photo of a pair that show a hex nut on one side, suggesting the pin is threaded. Maybe you can tighten them to see if that helps.
Rick
Tighten the bolt and nut so that the jaws stop from just gravity about halfway.