Inconsistent FaceTime data consumption

I've read that FaceTime averages 3mb per minute for an average which would be fine for me. However for me it's 3 for one call and to the same person 10 minutes later it will be 40 or 50 mbpm. I've tried to limit the background noise, excessive camera movement and I can't figure out what causes it to fluctuate so drastically. Any ideas would be greatly appreciated. Thank you.