The info given about the fleet only apply to AAR, not Europe. Subs are immune to AF without a destroyer present. With the presence of destroyers, subs lose first strike, nothing else.
If a german player takes a convoy center does his ipc value go up, becuase if it doesnt ive been playing wrong for a very long time, no wonder germany never lost.
The convoy center income is simply denied the Allie whose flag is in the center. You have been playing wrong, sorry.
Maybe now the Allies can erase that big donut in the win column? Welcome to the site.