Your weekly cashback cap is set by how much GNO you hold. Everyone starts with a 1,000 CRC base, even at 0 GNO.
From there, each 10x increase in your GNO balance unlocks another 1,000 CRC of cap 0.1 GNO gets you to 2,000, 1 GNO gets you to 3,000, and 10 GNO maxes you out at 4,000 CRC.
Within each tier the cap scales smoothly with your balance (no discrete jumps), but because each tier is 10x wider than the one below it, the marginal value of additional GNO diminishes the more you hold.
The first 0.1 GNO is the most efficient slice; the 9 GNO between 1 and 10 buys the same 1,000 CRC of cap as that first 0.1 GNO did.