Looks like they are using a much cheaper version of a fixing that works in that fairly standard size hole to save a couple of quid each corner. I guess having a selection of spanners to hand would make it less frustrating.
Std spanner is difficult to get into the hole cos of the lack of clearance. Pair of narrow nose pliers and a lot of swearing has got it reasonably solid.
Looks like they are using a much cheaper version of a fixing that works in that fairly standard size hole to save a couple of quid each corner. I guess having a selection of spanners to hand would make it less frustrating.