That's not what I was taught. It sounds logical but before I take an internet stranger's word on changing one of the likeliest things in life to kill you or those around you, did you read somewhere that this is a good idea based on research xyz or is this something you came up with?
IIRC I read it somewhere long after I learned, tried it, and it was so much better I was certain it was correct. All but completely eliminated my blind spots (I still turn and look, but pretty much never see anything that wasn't already in a side mirror, now). Turn them farther in and you're losing side visibility to gain redundant rear coverage.
[EDIT] I think I read about it in the context of correcting a common misconception or mistake, actually. Correct adjustment of the mirrors was described as watching a car leave your rearview mirror, and ensuring they show up on your sideview just as they're leaving the rearview—so if you can see cars on your sideviews before they're starting to slip off the edge of your rearview, you've got those adjusted too far in. For me, given how far back I put my seat, this ended up meaning I should adjust the mirrors all the way out in most cars. The idea is both to not have a gap in the sideview/rearview coverage, while maximizing side coverage within that constraint. So, if you can see cars in your sideview while they're still solidly in your rearview, that means you've got less side coverage than would be ideal.
BMW has a performance driving class and they teach the same thing - set them far away from your own car. It is a little disorienting at first because you kind of don't have a point of reference like you would normally, but it is totally worth it.
