I think it would be cool if all creatures had two detection areas adjusted by various factors.
1. The current cone for sight.
2. A circle that's generally smaller than the cone that surrounds the creature, representing: sound, smell, any kind of extrasensory or supernatural sensing the creature may have.
The size of 1. would probably be normal for most creatures, but could be adjusted for creatures with exceptional sight or blindness.
The size of 2. could be larger or smaller, affected by WIS and depending on if the creature is one that relies heavily on scent or hearing like a dog or bat.
Alternatively, you could assume that the creatures perception score already takes these factors into account. All creatures could have the same size areas for gameplay sake, but the perception v stealth would still balance going in for sneak attacks.