@SilverBullet:
#1: u can build 8 units in tokyo if u want 2 try flooding the north.(which is a bad strat imo)
#2: the islands have 4 production and japan has the transports it needs 2 take advantage of the island factories.(plus they produce units in the south, and japans aim should be india/persia imo)
But what if your fleet has to fight against the US ?
Your fleet cannot be in sz62 to protect the trannies and in the same time stopping the US progress somewhere else in the Pacific (and with CV + fighters, it’s quite easy for the US to put a pressure on several sea zones).
The main interest of IC on the main land is that you do not have to consider the position of your fleet. You will always be able to produce there and use the produced units. I already played a game as the Allies where I killed the japanese fleet but where Japan was far away from being dead, becaus of 3 or 4 ICs on the mainland. If you focus on Japan, EI or Borneo, loosing your fleet means game over.
I usually build in FIC, and very often in J1. Because this IC give the maximum of options : troops on the mainland that can fight either in China (Chinghai is at the same distance from FIC and from Manchuria) or towards India ; but whatever the Allies do, this will be usefull : 2tnk a turn towards Russia when facing a KGF, infantries if China survived for any reasons ; ships to fight the US ; ships that you cannot build safely in sz62 (see for instance the final of the last tournament where I built a lof of times a CV there because my fleet was in sz50 to contain any US move).
The only exception to the FIC IC would be when not built on J1 (that mean because of the bid or a R1 bomber so that I want to go after Burma and keep Philippines for J2 ; in such case, I build two trannies on J1 to be sure I can take everything I want on J2), and the US goes away from Pacific.
After that, it depends a lot of the situation : I like Manchuria if I sea that I need my fleet somwhere else and that there is some resistance in China / north way towards russia. I like East Indies when facing a KGF or a round 1 India IC. India can be the best second IC if qui safe. But I have no rule for that, all depend on the game.