Are you riding too light on the front wheel? Have a look at you riding style - are you loading the front wheel into corners? If you are not, then the shocks will feel too hard (front wheel will bounce). Maybe this is the problem. If you get a chance, get someone who rides a lot to have a look at your riding, ideally get some coaching. If your style is correct and you do ride "light" on the front then softer may be for you.
Attach a cable tie around the staunchen and slide it down a low as it goes. head out for a ride. At the end of the ride see how high it has traveled. The idea is that you use the full range of travel.
Don't be scared to soften them up. Note that suspension setting is not a science, each rider has preferences and styles that dictate you set the forks how you like them. The suggestions in the book are just that - suggestions. If you are 75kg, super fit and ride hard, fast and "heavy", you might need higher compression / damping, if you are 75 kg, and an unfit and slow and timid- lower might be better.
However, for XC you may decide to trade travel for efficiency - particularly on smooth, fast groomed trails - and stiffen the forks. I ride some local groomed trails with lockout because there is no advantage in having 50mm, let alone 100mm travel.