I take it from your comments above you are not going after Karachi or bombay. Why stop, from your perspective ?
You are correct. I don't plan to take (or try to take) either Bombay or Karachi. It may still be possible to take one of them at this point, but not both. Without both though, I don't think it's worth the investment. Taking just one right now (Bombay) would be expensive and time consuming, and even if I succeeded I might not be able to hold it until autovictory in 1943. Unless you commit to parking the KB in the Indian Ocean for the rest of the year, you can't prevent Allied buildup from getting through (and if the KB did stay here, how long do you think Japan would hold places like Noumea, Luganville, Wake, etc?) With the position I have now, I can still reinforce Madras and Calcutta without interference from the Allied navy (lots of torpedo-carrying Netties on Ceylon make sure of this.) Any fighting will take place over my bases, not his, so pilot losses should work in my favor. Tojos should be flying by the time he tries pushing, so I don't think there's any way he can get even local air superiority over me in 1942 here. Without any Allied air or naval support, I don't think he can take either city back. In this situation, he almost has to clear out Ceylon first. It's my goal to make that a very expensive thing to do. As for why I'm not taking the rest of India, that's simple. If I took it, I'd have to garrison it. Look at the garrison requirements not just for the picture I posted above but for the whole country, and you'll see what I mean.