From page 138 of "Manual Gearbox Design" by Alec Stokes,
"To prevent the face dogs slipping out of engagement while under load, they should be manufactured with a retaining reverse angle of between 5 degrees and 7.5 degrees on their mating faces. This means that the nose or outer end of the dog is the maximum width to be used when calculating the side clearance. However, even with this reverse angle, full face contact must be maintained."
"An angular side clearance of approximately 0.125 inch should be allowed betweeen the face dogs on the engaging dog rings and those on the free-running gears radially when viewed on the face of the dogs. Great care must be taken when designing these face dogs to ensure that full face contact is made when the angular side clearance is taken up."
The other paper I was referring to was "Manual Transmission Synchronizers" by Cocin and Walters, SAE? 680008. This is the best paper I have seen on the design of syncronizers, but I did not see any relevant information in the paper that you were looking for.