I've noticed most (like CRINA, Hibiki Shinji, and of course, Ritsu Kire) have their screaming pitches at a higher note. So being at a high pitch is most of it. The rest, is actually screaming. You can yell, like those banks do, or /scream/... if you want to get a... C02/Maiko/Sakebi-chan effect...
So yeah, pitch and power, I suppose!