I also mixed the shaft end thrust washers up when doing some head work a few years ago and thought much the same. The exploded diagram in the link (assuming it's the same motor as yours) has one at 0.2mm and one 0.5mm but doesn't say which goes where.
Maybe something to do with expansion i.e. vertical cylinder expanding a bit more?
https://www.motosparepartner.com/en/...camshaft_37933