I haven't built the Hog Bipe but most biplane designs are more concerned with the angle of the the wings and stabilizer relative to one another, not the physical distance. A spacing of wings +/- 1mm is probably insignificant.

Also, most designs establish a reference line on the fuselage that each wing and stabilizer angle is measured to independently. In doing it this way, one avoids a chain of insignificant errors compounding into a noticeable trim problem - sometimes called tolerance stack-up.