What I mean with the slightly gray area is:
Ice is detected on the back of the fan blades during walkaround, engine covers are put on for X amount of minutes (perhaps 10 min of your scheduled 30 min turnaround). You taxi out for remote de-icing in the same conditions that possibly gave you the ice on the way in. No blade de-icing is possible on a remote de-icing with engines running. Prior brake release a run-up is performed, no abnormal sounds or vibrations. Is the fan performing as advertised? My experience of having done run-ups during taxi in (to shed ice, to avoid having the hot air out) is that it doesn't always shed everything. Especially the innermost part of the blade has residual ice.