Does a higher fuel/air ratio in the combustor help prevent ICI? I would have thought not, but stand by to be educated.
According to our engine operability types, a higher fuel/air ratio provides increased margin for flameout due to an ice shed.
At least until the GEnx came along, the CF6-80C2 had most of the issues with ICI. Typical scenario was an idle descent in ICI - ice would build up in the booster (LP compressor), when the engine was spooled up for level off the ice would shed and quench the combustor. Although the engines always relit (auto-relight is basic on the 747-400 and 767 CF6-80C2 FADEC), there were some cases of HP compressor damage from the ice shed (note that this fundamentally different than the GEnx ICI, where ice accumulated during steady state cruise). Since the operability people believed increased engine bleed would provide flameout margin, mitigating action was to maximize engine bleed by turning on Cowl Anti-Ice in suspected ICI conditions (also wing anti-ice at lower altitudes - there was a proposal to use WAI at cruise altitudes as well but trying to bleed that much air caused other issues). Long term the FADEC s/w was revised to keep the stability bleed (VBV) open more and longer to remove most of the ice shed from the core. That apparently helped - it's been several years since we've had a reported ICI flameout on the CF6-80C2.