For most applications attaching the shear webs to the back of each spar is more than good enough, assuming a quality glue job.

I feel statements that back-of-the-spar shear webs provide a stronger glue joint are misleading. With an I-beam shear web the glue is only necessary to keep the shear web from moving out of place, there isn't nearly as much stress on the glue joint as the back-of-the-spar approach.