"negative brackets" is a truly great idea and would help many affected by poverty.
but that's not what adherence to UBI is about. UBI is about chasing an impossible utopia and burning ourselves in the process so that we have greater net inequality.
Stick to the plan. Call out anyone who tries to make UBI work by watering it down from our idealized end-goal as nay-sayers. Clutch to random hypothesis'.
It's the only way we can bludgeon them through democratic or revolutionary means.