Very late to the party here but I don’t think I’ve ever seen a J4 take down of India in about 200 games played. I can’t see the model which allows it. If you miss the J3 window, which the allies might be able to close with a UK1 Burma stack, you’re talking about a J5 attack, assuming a J1 DOW. J5 all the Japanese coastal troops from Jehol to Kwangsi are in range walking overland. That’ll kill anyone barring ridiculous dice or Axis stuff ups.
I’m not completely sure of the distinction between J3 and J4 other than 2-3 extra inf on India but maybe that small number of inf really does change things. Probably does given that you’re normally losing planes to take India down J3 if it isn’t evacuated.