Yeah, that compound interest is EXACTLY the reason you're NOT supposed to withhold quarterly taxes that you are clearly going to end up paying at the end of the year - and the EXACT reason they penalize you for it. I used to work on a 1099 myself, you can't do that, I don't care how good your accountant is.
So, again, either your accountant has found something else going on with you that even you don't fully understand, or your accountant is doing something super shady and hasn't been caught yet.
Or, as I say, the third option is that you're just talking out your ass.
Either way, anyone who takes your tax advise is doing so at their own risk.