Row 12 has no hard wall bulkhead in front, it is behind the last row of J seats (separated only by an upper curtain), so there is space under the seat in front. The reduced width is because of the trays in the armrests and the B and E seats have a pull-up IFE screen. 12D has always been my preferred seat in the A319/320/321. I do not find the width a problem, and even if the J seat is reclined, there is less restriction of personal space than with a Y seat in front. And you get served first in row 12.