Mushrooms are natural products, they can vary in potency even within the same batch... it's a matter of genetics - which makes them different just like people are different.
Also some people are less sensitive to psychedelics than others, it is apparently not really dependent on body weight which is a factor for a lot of other drugs.
It's too hard / a little early to say what the reason was in this case, you would have to try again some other time with 3 or 3.5 grams. I wouldn't personally take more, because that would be a good way to royally screw yourself if those are suddenly potent as opposed to the ones you have (assuming that is the case). After ~3 times and preferably not from all from the same batch (which still is genetically related), you should know if you are unusually sensitive or insensitive to mushrooms. It's not an exact science, but every time you take them enables you to say more and more accurately how you react, making it statistically less and less likely to be flukes.