I have always placed the caliper so it is behind the fork leg on my bikes, so that its mass is closer to centered on the steering stem, thus lessening the lever arm acting on it and magnifying its force on the steering. Moving it to the rear of the fork let makes the bike handle and steer better with less deflection at the bars--the same reason essentially all modern motorcycles put the caliper(s) behind the fork leg. Depending on the bike, that might be on the left, or the right side. On my 73 850 Commando, that ended up with my 12 inch disc and Lockheed caliper on the right side, with braided stainless line made to match.