There are a few things that can affect where the balance point of the plane is/should be.

1) The MAC is not necessarily in line with the wing root, depending on the taper of the wings.
2) The shape of the airfoil, and the location of the pressure gradients (the Wind has a very thin and wide wing, so the diffusion is slow and taking place over a very long distance which may reduce the sensitivity to CG location).
3) Like you said, a pattern plane with a long tail and small precise elevator controls will counteract the sensitivity that comes with moving a CG rearward.

These are just some thoughts off the top of my head... but yes, I would expect the tolerance of CG to be different on different planes, and the little pictures in my head seem to tell me the biggest factor has something to do with a ratio of the thickness:length, where a fat wing with a smaller chord would be much more sensitive to adjustments.

Will you have a chance to test fly it before handing it off? Can always add a little weight just for the purpose of honing in on the balance point - better to play it safe and slowly remove weight to see where the range is...