I must be missing something - from your previous thread about this FE2 and the FM2 it was to replace, I supposed that you were shooting with Nikon lenses, all auto diaphragm. To me, the idea that you had to shoot wide open to make focusing difficult doesn't add up, as an auto diaphragm lens would naturally be focused wide open, then would close to selected shooting aperture for exposure. It seems to me that overexposing with flash won't serve that aim, as overexposure is likely to blow out fine detail. There are distance and lens opening requirements for effective use of an SB-16 in TTL mode, which are described in the manual, and show in abbreviated form on the flash's calculator dial. Once you're satisfied with your lenses' focusing on the FE2, you can verify the SB-16's TTL exposure accuracy by shooting at apertures more in line with ordinary shooting.
Thanks and regards,
Vince