Blower controller aka FSU also FSR is the most common parasitic draw.
Final Stage Unit aka Final Stage Resistor
I don't know why BMW decided to have them stay powered with key off other than on some models you can use the "rest" function to blow heat with engine off and key out.
My X came with a replaced FSU at 128k miles. Wife's died about 115-120,000 (we got at 112, was the first repair).
There is a separate FSU for the back seat. I haven't had to replace either of our back seat FSU.
We have e53 I don't know how similar the FSU arrangement is on the e70 but I'd be willing to bet "nearly identical".
Search YouTube for e70 rear FSU replacement. (aka FSR even though it hasn't been an "R" for 30 years or something
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Some old habits die hard: perfect example, my father's generation refers to residential AC power as 110/220 vs. 120/240 and it has never been that in my lifetime though in 3 phase shop AC 220v is cross phase power so that is possibly where the 220 came from.
Anyhow one of my first posts to co was to figure out the parasitic draw killing wife's battery overnight and it was the front FSU hedge hog. I bought a knock off brand from Amazon and it's still going after 191,000 current miles so lasted about 70-75,000 not bad.
I will use knock off parts in non mission critical places where they are also easy to replace. On e53 it's a five minute job with no tools to swap out the front FSU.
The rear I understand is more work because of the location inside the console.
As far as how when sleeping: either the FSU gets power when sleeping or it's random power draw prevents sleep I'm not sure which.
Almost zero percent chance it's not FSU.