Kansas (2) - S4-E12
Visible crew/equipment: After Scorpius tells Braca that the future of Peacekeeper survival depends on him, it cuts back to Earth and when the Sheriff says, "I got the warrant. Let's go search that house," as the car pulls away we can see a nice reflection of a crew member and the reflector screen.
Chosen answer: It's never explained. John mentions a theory that his less technologically developed craft simply interferes with the wormhole less than the "superior" Vipers, but they never make a concrete determination on that point. But we also have to take into account the fact that Moya traverses wormholes with no ill effect as well.
Garlonuss ★