What you're 'attempting' to achieve is a maximum outer dimension of 38cm, from outer greeblie to outer greeblie. Most Y-Wing builders have discovered that this must have been a "rounded-up" number, since 38cm wide is the "official measurement" given in the reference books. So essentially what you're looking for is a dimensional width that can a.) hold all the greeblies, b.) "look" good and c.) come to within your happy tolerance of "exactness" depending on how you measure wingtip-to-wingtip. My personal take and "interpretation of the official measurement" is that the "smallest possible" width from outer greeblie to outer greeblie would be 37.6cm, and so my Tee-plates are designed to create that specific outcome. But that's just my two cents, and my wings are slightly "wider" than others, though not typically noticeable (to the naked eye) until you measure it.