The Boolean setting of $FCShowIEta determines whether
i \eta should be displayed in the
typesetting of propagator objects (except for FADs) or not.
This setting affects only the TraditionalForm typesetting and has
absolutely no influence on the internal handling of propagator
denominators in FeynCalc.
$FCShowIEta
SFAD[{p, m^2}]\text{True}
\frac{1}{(p^2-m^2+i \eta )}
$FCShowIEta = False
SFAD[{p, m^2}]\text{False}
\frac{1}{(p^2-m^2)}
$FCShowIEta = True\text{True}