I was somewhat interested in the answer as well.
I have been using "Cross Fade (Aggressive) - 2s" but found that to be a bit much, and moved it down to 0.5 seconds. Still not quite what I would like.
I thought Gapped Fade should work the way you expect. So I just tried it with various delays up to and including 16 seconds. Regardless of the setting, MC seems to finish the song with no fade, then immediately launch into the next song, when transitioning without user input. When I hit the Next button, with 16 second Gapped Fade, I get a very slow 16 second fade on the song playing, no real gap, maybe just a beat, and then the next song starts. I tried turning off "Do not play silence (leading and trailing)" and "Use gapless for sequential album tracks", but neither changed the behaviour, although the listening result was different due to the full length of the track being played, including silence at the end of a track.
The Wiki says:
Gapped Fade
Provides a smooth transition when switching between tracks without any overlap of the two tracks. (Correct, there is no overlap.) If the first track finishes naturally, there will be a small gap between tracks. (Correct, there appears to be a very small gap, but with "Do not play silence (leading and trailing)" set to remove silence, this can be hard to see/hear.) If there is a manual track change where the first track is somewhere in the middle of the song at track change time, the old track will fade out, then a little silence will be heard, then the new track will begin. (Correct. This appears to be the only occasion that the time delay set with Gaped Fade is used, and it sets how long the fade takes before a track changes, rather than the size of the gap between tracks.)
So I guess MC does do what the Wiki says. But it isn't what I expected. I was expecting the time associated with the setting to be the gap introduced, similar to the "Standard (gapped)" setting.
It seems that "a little silence" with this setting is a fixed amount, and not related to the number of seconds in the setting. Also, fade is only used when a manual track change is initiated, because if the song runs to the end it probably has its own fade built in. However, that fade can be shortened when "Do not play silence (leading and trailing)" is set. Perhaps try Gaped Fade with this setting off, to get the normal fade built into the recording?
It actually makes sense that a fade is only required if a track is manually changed, so that the existing song doesn't suddenly drop out. But also, there is no need to fade in the new track, if the track has some silence or built in volume increase up to normal volume.