Since the OP has had their sUAV for a couple of days, let us assume they are not Part 107 licensed,
It is my opinion that in that case they are operating under the blanket COA issued under Part 333, and that is where the 400' limit comes from.
I'm not the Drone Police, I'm just expressing an opinion.
It is all fun and games until someone gets knocked down, knocked out, or knocked up.
I find some of these FAA regs to be complete and total BS, and maybe once or twice I may have technically been in violation of a few of them, if you decide to interpret the regulations in a different way it is no skin off my teeth.