Ok, I changed test query to:
select min(pb.metalHeight), pd.pot.room.smelter.name from PotDates pd left join PotBath pb on pb.potDates.pot.room.smelter.smelterId = pd.pot.room.smelter.smelterId and pb.potDates.pot.room.roomId = pd.pot.room.roomId and pb.potDates.pot.potId = pd.pot.potId and pb.potDates.date = pd.date group by pd.pot.room.smelter.name

and the resulting SQL still contains unnecessary left join and moreover it's not valid anymore, because it's trying to use table which is defined later in previous joins like this:

LEFT OUTER JOIN PotBath potbath1_
ON (room4_.Smelter_ID    =room6_.Smelter_ID
AND room4_.Room_ID       =room6_.Room_ID
AND pot3_.Pot_ID         =pot5_.Pot_ID
AND *potdates2_*.Date_Trunc=potdates0_.Date_Trunc)
LEFT OUTER JOIN PotDates *potdates2_*
ON potbath1_.Date_Trunc =potdates2_.Date_Trunc
AND potbath1_.Pot_ID    =potdates2_.Pot_ID
AND potbath1_.Room_ID   =potdates2_.Room_ID
AND potbath1_.Smelter_ID=potdates2_.Smelter_ID

and the condition in PotBath join is very strange. It should reference the table itself but is using other tables in join condition