Why do replacement main bearing sets have 6 bearing halves with oil grooves?

I am in the process of rebuilding an ALH engine. The main bearings that I bought have an extra grooved bearing half. I have read many threads about this issue and people either suggest to put this bearing on the cap side of journal 4 or 3.

Nobody seems to have a good reason for this. The only explanation that I have seen suggests that placing the extra groove on main #4 allows for extra oiling to rod journals 3 and 4. How does having an extra oil groove on main journal 4 give more oil to the rod journals?

My first thought when I saw the extra grooved bearing was that it was for main journal #3 as this journal does not have an "oil hole" on the crank....

What was the manufacturer's reason for changing the bearing sets from 5/5 to 6/4 (grooved/ungrooved)?

In the very first 827 block gasoline engines ( i know you have a Diesel,but they use the same main sets) the cranks were not x-drilled
And #3 main,rod 2 and 3 got an extra feed of oil from the 360 groove on #4 main
Since then,the bearing manufacturers (or VAG for that matter) has not bothered to change these bearing sets,until around year 2000
Then some clever guy maybe found that "hey,why the heck are we still running 360 groove on #4"

Sounds silly I know
But there is no other way to explain this better
It makes no difference for your engine if you run 5/5 or 6/4
It makes no difference where you put the 360 either