Before 1.5, JAP used to DOW USA, and not the PHI. This way you could have easily avoided dragging PHI into WW2, having a neutral airfield right next to the Japanese AO. In 1.5, Japs did not create enough World Tension for me to even be able to go for War Plan Orange, so obviously, I couldn't get PH Gambit too. BUT they did attack PHI, and it dragged me into the war as well. Much better than 1.4, IMO.
They also sent two naval invasions at me, to capture Wake and Midway. I think they had them pre-planned before they DOWed, beause I did not set up air superioirty patrols before the war started, and set up air cover only after the fact. And, if I understand things correctly, this allowed them to set naval invasions into motion. You couldn't do that when the enemy has air superiority in the region, right?
Anyway, it's a really good thing that Japs start by DOWing PHI. One thing Jap AI missed tho - they did not pre-planned PHI naval invasions, as per history. But I haven't played much after the war began to see if they would send anything there later.