@SS:
:cry: KISS :cry:
Said otherwise, to lose IPCs in Convoy Disruption Phase, the enemy need to capture one of your originaly held valueless Islands AND put in the surrounding SZ a single submarine (-2 IPCs) or warship (-1 IPC).
Those penalties cannot be cumulative, even if there is more units in SZ, it is either -2 IPCs or -1 IPC, no more no less.
For instance, once Guam taken by Japan and having as many IJN Subs as you want in the surrounding SZ of Guam, it will cost 2 IPCs to US until all IJN Subs move elsewhere or are sunk by Allies.
A different NO, simpler but probably costlier to original owners, based on my suggestion made earlier:
All valueless Island groups controled by at least one stationed unit (Ground, Air, operational Air Base or Naval Base) gives 2 IPCs.
But cost 1 IPC to any original ex-owner, this penalty applied during Convoy Disruption Phase of this ex-owner.
http://www.axisandallies.org/forums/index.php?topic=34839.msg1355089#msg1355089