In real terms it's hard to imagine how a cowl made of fabric could be made or sculpted to form something of a scowl over the eyes as was done with Christian Bale's mask. Probably not impossible, but hard to imagine.
Having the lower face exposed could also be a seen as a means of expressing friendliness towards those not intended to fear Batman, such as innocent civilians and children.
Of course, he could just forego growling at them when he speaks.
