I guess it is possible to increase the spring pressure by loosening the knob, but it seems overly complicated. I am not aware of any pressure sensative prop valves like that. Adjustable and non adjustables I know of are offshoots or knock offs of a Kelsey-Hayes design put in production in the mid sixties.
The spring has to put pressure on the piston. Increased spring pressure increases the knee point=increased line pressure.
There is a brass valve being sold as a proportioning valve which works the other way. You can find it at some hot rod vendors. It looks cool, but isn't really a brake proportioning valve. It's more like a faucet. It increases or decreases flow at all times. Not designed or recommended for brakes.