As a fighter over the Pacific, there was a lot less ground fire to contend with.
This brings up the old argument of twin engine survive-ability. Does twice the target area of a twin engine aircraft confer any added survivability? Psychologically I'd say yes but in in reality, I'm not so certain.
In a ground attack role having to contend with concentrated German 20mm and 37mm flak, the P-38 was at a disadvantage versus single engine fighters due to the Lightning's overall larger target profile.
However, the P-38's concentrated firepower enabled the pilot to hit whatever he was aiming at from up to 2,000 yards in a shallow attack and even greater distances in a dive.
Whereas, single engine fighters had to close to whatever distance, 100 yds, 250 yds, 300 yds their wing guns were sighted to converge at.