yeah fill as much as mounting angle will alow and a smear on the gasket too. the theory makes sense but if its actually useful? i dont know.
I was also told by some random bloke passing by told me if you open a radiator cap when the engines warm-new style with the recovery bottle cap not on the actual radiator- with the motor running that it will depresurise and not flow over with the pressure. i tried this method and guess what-didnt work!