I find that Humbrol matt is about as matt as it gets.
As for wet vs dry, when you spray any paint, it looks 'wet' when first applied, this means that the paint still has enough solvent, and is the right thickness, to smooth out before it dries. The line between 'wet' and running down the model in big drips is sometimes a little hard to get right!
By avoiding the 'wet' look as you spray you are letting some fo the solvent dry off in the air between the airbrush and the model, and the paint is going on in a mist that is not thick enough to look wet. What this acheives is more 'tooth' as the paint does not have time to smooth out on the model before drying.
This ensures that your matt coat does not become satin through being too smoth.