Apologies if this has already been addressed elsewhere.

How do you determine the difficulty of a Gain the Advantage check if both parties are flying through difficult terrain?

Gain the Advantage states that its difficult is determined by the difference in speed between the two vehicles. So if both are flying at speed 3, that's an Average (**) check. But piloting checks through stellar terrain are calculated from the ship's total speed and half its silhouette, so if the vehicle in question is Sil 2 that's a Hard check (***) upgraded once.

Anyone any thoughts on how to address these two separate ways of determining difficulty? My gut instinct was to go with the terrain rules, which I think are better thought out, but then you're not giving anyone any benefits for going faster, so now I'm not sure. Any advice on this would be greatly appreciated.

Thanks in advance.

Check out the "Celestial Hazards and Difficult Maneuvers" section on the same page as the stellar phenomena page (254 in AoR). The rules you mention are only for navigating difficult terrain, doing things inside that terrain is covered by setback dice based on how bad it is (with an upgrade or two based on speed).

Hinklemar nailed it. You only use the difficulty for navigating difficult terrain when doing something that used to be simple difficulty (and thus didn't normally need a check) such as moving. Otherwise, you use the setback dice.

Ah, OK, that answers the question. Missed that completely. Thanks.