Thanks so much for remembering!
Unfortunately, my issue seems to be that the 'Win 10/Store' layer of the OS can't detect the drive at all. Legacy layer is fine. Don't know why, all my data drives are connected via the top 6 Intel SATA 6 ports, rather than the later two ports governed by my Maximus VI's Marvell controller.
The one time it did detect my EVO was when I detached my biggest drive and filled the Win 10 OS drive, then it gave me the option. Once I put everything back into place, the drive was gone. I had to manually delete all the files at the root install folder.
Maybe the coming fall update will finally fix the problem ¯\_(ツ)_/¯