Ride at the speed long long enough, SOC will go below 40% and ICE will come back on, then MPGs will melt away quick.
The AC relies on that massive front radiator (condenser) for cooling. Personally, I don't use any grill block once ambient temps are staying above 10C. With ambient temps below 10C, I'll typically block 50% of the lower grill. If ambient temp is steadily below 0C (rare here) I'll sometimes 100% block lower. Maybe.
Personally, I don't EVER block any part of the grill......EVER. If done wrong, it can actually increase your wind resistance and do exactly the opposite of what you want.