It will be same here, if manager wont attending even with full stadium home team will lose advantage
And as you say in greek league small teams have smaller support than big ones but in real life football fans are just one part of home advantage. Weather condition, wind, size of the field, quality of grass etc affect also, condition where home team have expirience of playing on that conditions, all that affects but in game we have just fans and till all that be avaliable to set we need to balance supporting part