Cleaven, I don't think anyone knows why it works sometimes and other times it doesn't. Last night, for example, Jeff and I tried a co-op in 8,19 (I think). The DV was at 10, but it had some ai counters in it left over from previous failed attempts I guess. Anyway, as in the other night with Doggy, a Courier Intercept mission dropped the DV. Sadly, Jeff didn't have time to run any further missions on it.
Just thought, I probably haven't publicised the details of what happened to Doggy and I the other night. We hit a neutral hex (can't remember which one now), and for twice in a row, with Courier Intercept, the DV dropped. We did this by killing every enemy ship. The 3rd attempt, Doggy captured one, and the DV didn't drop. Thereafter, the DV failed to drop (2 more attempts, reverting back to destroying all ships). Other missions that we tried did not affect the DV. So it seems that there is something in the Courier Intercept mission that works more often than other missions.
I will try and get on again tonight (going out tonight to see X-Men2) and try some more missions on 8,19, and will report findings here.
Btw, the missions with Doggy are the first ones that I have ever seen where the DV has dropped AFTER the first attempt. So some sort of progress is being made here. As to what has caused this, I have no clue. It may have something to do with the specific .gf settings that Tracey suggested we try, or it may be something in the Courier Intercept mission itself, or maybe a combination of the two.