I too had an over-aggressive rad/grille block setup for a while this winter.
A cardboard shipping box, when completely flattened, provided a near-perfect cover of the radiator.
In my case, the rad is behind the A/C condenser, which allowed the cardboard to completely cover the radiator as a sandwich. Consequently, even in temps in the single-digits F, caused the FWT to rise to "levels of concern" and required a robust heater blast to maintain proper cooling.
The plan is to hack away at the center sections of the cardboard to allow some flow (right now I pulled it entirely, until I get a "Round Tuit" to cut and re-install the cardboard.) On cold-starts without an EBH hookup, it takes quite some time to sufficiently warm up, especially with the Arctic blast lately. TC engagement is still a problem...
On nearly all brand new cars I've tested, the torque converter will engage when the coolant temp is literally 10F and sometimes below! What gives? I have to have 190F+ and IATs in the 90's for that to happen. Argh.
At any rate, there is a compromise, but significant testing can only reveal what works best in each individual application as far as the block is concerned.
-Rick