my standard java fern is about 8 inches tall and 1.5 inches wide at the widest point. i have no experience with windelov or narrow, though narrow gets about the same size except half as wide. A word of warning: even though they are said to be "slow growing", each week i have to harvest about 1/8 pound of baby plantlets (and i dont have that much in the tank). i have some babies on wood, and in a month they were half as big as the parents.
good luck