Yet, they killed the Jews in occupied countries as well. Shockingly, the Nazis were the least efficient at doing their genocide at home where the support was highest.
I'm not sure that's accurate. By sheer numbers, it's pretty much Poland taking the lead and that's because the rest of Europe killed/displaced their jews in previous events (turns out hating jews is basically an European tradition).
Statista agrees you with in that comparing the deaths by country to its initial population by country shows Germany around 32% while say Poland is 75% [1]. But the big problem with that is it omits emigration; I would suspect jews in Germany saw the writing on the wall and left. The Germany jewish population dropped from 525k to 37k [2] (with 165k dead [1]) which means 323k jews must've left Germany while Hungary dropped from 445k to 190k (with 270k dead) which means -25k jews emigrated (aka 25k jews immigrated).
So it just appears that Germany is less efficient because the local jews emigrated to other countries where they were then killed juicing those countries stats.
