No matter how square you think something is, a couple mm in either direction can really throw things off. Luckily OpenPnp has a setting for this. It's easy to figure out with some graphing paper.

Here are some other ways to make things more accurate.

I found some auto feeders I liked here. There's a lot of parts to assemble, but there's a lot of well thought out features to make sure the tape is fed and peeled consistently. Check out the site linked above for details.

This is the part that actually peels the tape with the N20 motor:

Here are the assembled feeders mounted to the frame in the first thought of where they could be placed:

Here they are all wired up:

To the controller:

Which also has two vacuum sensors.