For me, it was less an issue of the penalties for environmental modifiers, those were pretty straight forward, apply the worst category, if there was a tie apply the next penalty up, it was the mitigations. What applies and how much and what does that make the worst category and by how much.
Tracer ammo reduces wind and range by 1 row, but only it it's at least the second penalty row, sunglasses reduce glare by 1 but worsen lighting, ultrasound reduces visibility by 1 and ignore lighting, but only within 50m, and so on.
If i got bogged down, it was here.