Followup:
I stumbled over Topp's KTB -
http://www.uboatarchive.net/KTB552-6.htm
Page 1 - 23/24.10.1941
He loaded 2 Atos and 12 Etos into his 552 VII C - and consequently the Atos were to be stored in the deck containers. So 12 Etos were stored inside the pressure hull, in all available tubes and reserve positions - aft as forward - above and under the floor plates.
Every reserve torpedo storage space was accessable for charging/venting Etos as for greasing the drive shaft and refilling compressed air for the gyros and the depth keeping device.
Maybe they had to lift/shift the torpedos around to service the eels stored under the floor plates (+ center forward). But they definitively stored Etos there too.