Thanks. Also had it confirmed by the hotel now.
I booked it this morning but I'd missed your tip and I'm not sure I've booked a premium room! Got the best price booking via Tripadvisor with the hotel directly. Unfortunately, the booking confirmation doesn't mention the room type but I remember getting the 46sqm room.
Size is a big part of the reason why I'm paying a premium versus the Park Plaza Soi 18 (which I almost booked yesterday). Couldn't find their room sizes but the cheaper (superiour, deluxe) rooms looked smaller than even the basic 39sqm room at Legacy Suites.