A little more detail on the background of your question might make a more appropriate answer possible. Is it civil, or military aircraft being considered?
The aircraft I work with is a medium twin, used by the military for paratrooping and by civilians for skydiving. The background is that there were recently three aircraft related parachuting fatalities, which is causing us to look more closely at parachute clearances.
Two of the fatalities involved another aircraft type, often used for military paradrops, where canopies snagged on an antenna and tore. (The "blamespotting" for these is complicated by the fact that neither victim deployed their reserves, leading some to blame the paratroop training). On review it was found that it was fairly common for canopies to contact the aircraft on deployment, but that there were usually no consequences as the contact zones were relatively smooth.
The third fatality involved a freefaller who contacted the horizontal stabilizer on one of the aircraft I am responsible for. Although the inquiry is not yet complete, I believe that this particular jumper adopted a specific body position on exit, which resulted in his exit path being substantially different to normal. On review what did become clear was that there is a very wide range of possible exit paths - jumper mass can vary considerably, and the body position adopted can cause dramatic variations on trajectory.
I initially contacted our local CAA to inquire how they cleared aircraft for parachuting. They referred me to the national parachuting club safety officer, who in turn suggested that their clearances are mainly based on the opinions of experienced jumpers. They had no formal standards against which they judged the safety.
I also looked through various military standards - including the old AVP 970 documents. the military seemed concerned about 'crossover", where paratroopers are exiting through doors on oth sides of the aircraft, and may collide behind the aircraft under canopy. The A400M people did a lot of simulation work on this issue. However I can find no standard or reference that specifies the acceptable clearance margin (or acceptable contact / required smoothness) between canopy and aircraft. I suspect that it is handled subjectively - a lack of incidents or accidents resulting from contact is taken as proof of acceptability.
I believe, however, that the aircraft to jumper relationship deserves a lot more attention...
I'm coming to that conclusion as well.