1/32" is a good target. "Touching" is not so good since it may result in scratched paint and negative cosmetics -- if that is important to you. Also keep in mind that paint thickness will take up some of that clearance. Canopy air leakage along the sides is addressed by weatherstripping and inflight the canopy sides tend to bow out and up due to air pressure.
David Heal - Windsor, CA (near Santa Rosa)
EAA #23982 (circa 1965) - EAA Technical Counselor and Flight Advisor; CFI - A&I
RV-12 E-LSA #120496 (SV w/ AP and ADS-B) - N124DH flying since March 2014 - 740+ hours (as of Mar 2019)!
through June 2019.