Outside Europe where transition altitudes/levels are as high as FL180 you MUST set STD or QNH at the transition altitude/level and not before
Do you have a reference for that?
It seems that In common with many others our Ops manual is very prescriptive in requiring STD to be set on the PFD once cleared above the transition altitude regardless of whether the TA is low or high...(the standby alt is left on local setting until passing the TA).