So make that a thing that's actually part of the Traveller rules? Because it's not. Not even in T:NE which actually used reaction drives. It also uses the "roll randomly to determine how long it takes to get from world to world because no one expects you to have an orrery for every system" with no suggestion that skill plays any role in that.
In Classic Traveller, Astrogation didn't do anything and no one needed to have it (and it was just called Navigation). In T:NE, you had to make an average Astrogation task before you were allowed to jump, but it didn't otherwise affect the jump itself. You made a separate astrogation check to determine arrival orientation, which was expressed in fuel usage of the reaction drives to reach orbit (normal amount, 10% over, 50% over). You also were supposed to make astrogation rolls to successfully maneuver from orbit to the 100D mark and vice versa, but then T:NE was a game where you had to make an engineering check to make the M-Drive turn on at all
I'm just saying put this stuff in the game if players are expected to know what the skill does, so they can use it. Yes, you can house rule all kinds of things, but If Astrogation is used rather than Sensor ops to analyze the system, then say that. If Astrogation is "space stealth", then say that. If it can affect how long you are travelling in real space, say that. Give rules. Is a gravity slingshot the default way to travel in system? A special case that makes it faster? How much faster?
Btw, the one adventure that actually has a gravity slingshot in it (Theories of Everything) uses Pilot for the whole exercise.

It's possible that the astrogation check was made off screen by NPCs, I suppose.