A clean channel sand can be near one. A thin-bedded reservoir can be well below one half. It is a fraction, not a thickness. Multiplying it by the gross thickness returns the net.
Say which net is meant. Net reservoir, the porous rock, gives a larger ratio than net pay, the porous rock that also contains hydrocarbon. A net-to-gross used in a static model and a different one used in the volume calculation will not reconcile.