I invoice for the maximum number of hours I can get away with, not sure what is the benefit of using the actual number of hours worked?
It sounds like you’re fraudulently reporting hours you worked and stealing from the client.
I know what I'll get paid, and the client knows what they're going to end up paying for the work that's been scoped out. It's up to me to determine whether I'm managing my time/rate correctly to make it a value for the client and that I'm getting what I feel I'm worth.