@Baron:
Sometimes, defenders are caught off-guard on the airfield but once the interceptors are in the air, they get the advantage:
they are flying over a known homeland territory,
pilots have spent less time in the air, are more concentrated and less tired,
planes have plenty of fuel and less restricted on combat maneuver than attacking escorts fighters,
and defenders can stay longer in the area to patrol against slower or lost attacking planes,
all this can be exemplify by the UK’s pilots experience known via the air Battle of Britain in 1940-41.
This is correct, and since Baron mention the Battle of Britain, that was a special case since the planes had to cross the Channel, giving the German fighters only 10 minutes of operation over Southern UK before they had to return home again. The British fighters could of course stay up in the skies for hours, since their Airfields were close. And since the British defending fighters had plenty of fuel and time, they could fly high and attack from out of the sun. Germany would attack with more than 2000 planes, but because of the long range, they had short time on the target, giving the 700 defending British fighters the advantage.
But with that said, when the range was the same for both escorts and interceptors, the battle value would even out. To house rule this get complicated. You could let a fighter hit on 3 or less in his own territory, and modify one less pip for every space it moves. So a fighter that start in Normandy, lose one pip over the Channel and one more pip in UK, giving it an attack value of A1, while the UK fighter in UK roll a D3. Same when scrambling. If the UK fighter need to scramble into an adjacent seazone, it lose one pip because of the movement, giving it a defend on a D2.