Another example.... I work with an old guy who's a retired pro and he doesn't slap the mitts back because he wants me toreach and it hurts his joints a bit, so when I jab his mitt it sound like I'm hitting nothing but air. But there's a new trainer at our gym who slaps back and when I worked with him the first time I was getting TONS of snao without putting tremendous effort into it but rather perfect form and he said "damn, that's a beautiful jab you got there." But again, on the bag it's merely a quiet thud. You'd think a little boy was hitting it. So don't worry about it. Strive for form and bringing it straight back to your cheek.