From: Winnipeg, MB
Well, you could swim under the Golden Gate bridge .... oh, wait, you mean your subs!
The strait between Formosa/Taiwan and the Chinese mainland is a natural channel, as is the deep sea hex just above Batan Island, between the Philippines and Formosa. If you are hunting warships and amphib TFs, sit at the choke points between his route of approach and your bases. Early on, you can get away with putting subs in shallow water because Japanese ASW is so bad.
You could also try near his latest conquests since there are usually follow-up convoys of support troops and supplies.
Also keep an eye on the Detection Level of your subs. Once spotted it is easy to route traffic around them, and even if the TF has to pass through the same hex as the sub it seems to spot the sub and force it to dive more often if the sub has been detected a turn or two before. If I have a DL of 3 or more on a sub I move it at least 5 hexes for a few days and bring it back if I'm still interested in the original patrol area.
There are differing opinions on patrol areas - I like to keep mine small and focused, with little cruising around while others swear by the "patrol around target" setting which sets a random shaped zone over a large area. They put several subs in the same are with that setting to get coverage. As "godochaos" you may prefer the latter approach.
No matter how bad a situation is, you can always make it worse. - Chris Hadfield : An Astronaut's Guide To Life On Earth