thats what Nevin specifies in the directions
for a CPU with an IHS, you need 1 to 1 1/2 grains of rice of a BB-sized dab of it on the IHS
the science behind this is AS5's break-in period, part of that period is the spreading of the thermal compound to form a micro-thin layer of it across the IHS, and during this process, it will fill microscopic gaps in both the IHS and the HS base as it spreads, because of the way it is forced to spread out, its forced into these microscopic gaps, and that helps increase cooling capacity
plus, note that the core is not the size of the entire IHS, so you're just wasting compound if you spread it over the entire IHS
i used to do the razor trick like you, then i finally read the AS5 directions, and gave it a spin - my load temps dropped 8ºF from the razor spread technique after about 2 weeks worth of normal CPU use (plus the usual daily hour of P95 torture test - don't ask, its a habit
)
load used to be 112ºF, now its 104ºF
the 104ºF is also with a GPU block added to my loop, along with DUAL P95 torture tests (the old 112ºF was done with a single instance of P95 TT)