FWIW the coolant bypass whether it's integrated into the block or an external pipe, is always a narrower bore than main rad cooling circuit.

This is the case with conventional cylinder head or rad return thermostat location.

Richard

2018 Roadster 3.7
1966 Land Rover S2a 88
2024 Royal Enfield Guerrilla 450
1945 Guzzi Airone