Rocker Trouble

So I’m new to surfboard shaping and I’m confused on how to decrease nose and tail thickness without increasing the rocker. If I start sanding away the bottom of the nose, the rocker will start to curve upwards more. How do I prevent or minimize this as I’m aiming for a small wave board with a relatively flat rocker. Do I take foam off the top instead?

You can either take the same amount of thickness off the entire blank (retains the same rocker) or you can work off the deck and blend that together.