Southwestern corner of AM35, task force of at least 3 battle ships, at least one heavy cruiser, and a minimum of 4 DEs.
I have had luck with task forces in the following area.
Draw this on your map with the ruler tool...
Start in the SOUTHEAST CORNER OF AM33 and draw a line to the SOUTHEAST corner of AM27... from there draw another line to the SOUTHEAST corner of AM72.... from there draw another line to the NORTHWEST corner of AM72.... from there draw a line to the NORTHWEST corner of AM27 then another line to the NORTHWEST corner of AM33... then finally another line back to the SOUTHWEST corner of AM33. you should end up with an angled corridor. Hunt within this area in 1939 - 1940 that i know if.
On my last patrol i ran into a heavily escorted carrier task force in this corridor fired 4 torpedoes at an illustrious. one torpdo struck an escort on the way to the carrier and everyone started zig zagging but the carrier must have increased her speed because one of the three remaining torpedoes struck her in the midsection and a second one hit her aft, the third narrowly missed aft by several meters. she listed hard to port and kept on trucking for several miles before finally sinking.
I have had much success in this area of the world.
mostly warships into and out of the med i would guess??
Edit: now that i review my SH3 commander files it was an illustrious fleet carrier and a Fiji Class Cruiser, then the immediate next patrol i encountered the group of battleships. very rich hunting grounds... also i should mention that there is a natural "choke point" where merchants and convoys tend to bottle neck into the St. Georges Canal in and around AM52/53 patrol those grid squares slow and submerged for several days and you will return to port with many pennants! Hydrophone contacts everywhere, but beware some of that area gets pretty shallow so i recommend hit and run tactics if you can.