Yeah mono conversion is not easy to get right. I never use the auto settings. I prefer to use the Channel mixer (set to mono obviously) and adjust each RGB channel until I got the result I like. Depending on the colours in the shot I tend to move one of the RGB channels to the left whilst moving the other 2 towards the right (note: Ansel Adams type effect are just extremes of these adjustments). One final tip too is to apply a cross-processing effect if you are converting to mono, sometimes this can add even more punch (used both these techniques on my shot today). Anyway that's just the approach I have found over time.
Good luck, look forward to more mono's, I love em