B737 minimum maneuver speed amber band changes with speedbrake

[Too Few Stripes]

I think there’s some confusion in your initial post, the two different amber bands (upper and lower) were used interchangeably.
the upper amber band shows the flap limiting speed for the next flap setting using the logic you stated of 1 5 15 30 (40 if set on approach page). With flaps up the logic of the upper amber band is different.
the top of the bottom amber band represents minimum manoeuvre speed for the current config.