Note sure if this helps.
From Annex I to Commission Regulation (EU) No 1178/2011:
FCL.910.FI FI — Restricted privileges
(a) An FI shall have his/her privileges limited to conducting flight instruction under the supervision of an FI for the same category of aircraft nominated by the ATO for this purpose, in the following cases:
etc
From Annex VII to Commission Regulation (EU) No 290/2012:
ORA.ATO.210 Personnel requirements
(a) [...]
(b) Chief flight instructor (CFI). The ATO providing flight instruction shall nominate a CFI who shall be responsible for the supervision of flight and flight simulation training instructors and for the standardisation of all flight instruction and flight simulation instruction. The CFI shall hold the highest professional pilot licence and associated ratings related to the flight training courses conducted and hold an instructor certificate with the privilege to instruct for at least one of the training courses provided.
From AMC/GM to Part ORA:
AMC2 ORA.ATO.210 Personnel requirements
QUALIFICATION OF HEAD OF TRAINING AND CHIEF FLIGHT INSTRUCTOR
(a) [...]
(b) Chief flight instructor (CFI)
(1) The CFI may delegate standardisation and supervision to the flight instructors. In all cases it is the CFI who is ultimately responsible for ensuring quality and standards.