Hmmm, I would say that getting a good bond between web and spar is more important that getting the web at the spar centerline. In other words, a poor glue joint will drastically reduce wing strength while an off-center web will probably have very little effect. Remember that you have a lot of ribs keeping things lined up fairly well.

I have built glider wings as BillHarris describes. 1/8x3/8 spruce spar, 3/8 vertical grain balsa web, carbon filament wrap. This was eight years ago. I have no idea what "modern" design details are.