Our master closet is set up almost exactly like yours, even to size, its 18' long x 7'7" wide. We chose to put the mirror as in Option B. Love it there. We also chose to light the closet enormously - there are 3 huge led 24x24 flat lights on the ceiling. They are not decorative, but enormously functional. The fixtures themselves disappear against the white ceiling; but everything in our closet is lit very well and accurate color-wise. I was so tired of dark closets and trying to find things. The lights are on a dimmer just in case, but mostly we leave them at full on. Got the lights at Home Depot, regular stock item.
https://www.homedepot.com/p/Commercial-Electric-2-ft-x-2-ft-48W-White-Integrated-Edge-Lit-Flat-Panel-T-Bar-Grid-Flush-Mount-LED-Troffer-with-Color-Changing-CCT-FP2X2-4WY-WH-HD/304258310
Note - the architect thought a three way mirror would work very well. We might eventually switch. I had an existing 8 ft framed mirror and chose to use that initially.
You also might want to consider making the door from the closet to the bathroom a pocket.
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master shower
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