Thank you for the response.

The wing tube is not visible as the wing is completely covered in one piece . So it not possible to use it a starting point.

Also a well respected pattern flyer at our field ( Black Dirt ) said that there are many planes that do not balance on the spar, thus before or behind it. He also said that this was especially common, but not universal, in acrobatic planes with tapered wings. Which this clearly is .