Here's an easier way to "eyeball it".
I'll demonstrate on this lovely little breadbox I picked up for 5 bones.
After the box was all good and painted I was ready for vinyl.
I have my sticker with the transfer tape still stuck to it.
I cut an edge of the paper so that the tape is exposed on the top, but not the vinyl sticker.
To make it even easier, give yourself a much larger piece of blank transfer tape. Mine is too little.
Now simply tape the sticker where you'd like it to be.
It's easy to remove and adjust it if it doesn't look right.
Once you've found the right spot, hold the top of the tape to make sure you don't lose your spot.
Next lift up the bottom and remove the rest of the backing.
After the backing is removed, press down the rest of the vinyl.
You've got a lovely little vintage breadbox without badmouthing any vinyl.