The required scantiness will vary depending on the thinckness of the fabric and thread used, and also how you press, open or to one side. I use a 60 weight cotton thread to piece (YLI) which takes up little room and I ALWAYS do a test block and measure, check points etc before proceeding. My needle position can vary a click either way depending on the fabric, etc, etc. Depends how pernickety you are I guess - I'm VERY pernickety! LOL