The above info is right. Although I doubt having the transmission in neutral vs. park will make any noticable difference.
I suggest you choose a temperature to check the oil, hot or cold, (preferably hot) read the oil level at that temp everytime and don't worry about the other reading.
Make sure the stick goes down all the way into the trans each time as there is a lip at the top of the rod for sealing the oil check tube when the stick is in the trans. This lip can make you think the stick is all the way in when it is not.
Always be sure the car is as level as you can get it when you check the oil. You may have to check it at your local gas station or business park if your driveway is not almost perfectly level.
The amount of oil you are adding and removing to get correct reading seems excesive to me.
Is the dip stick bent? It can go in two ways, check the level indicators printed letters to find the "top" side, and then always put the stick in the same way. If too bent, replace the stick if you cant straighten it out.
The 'Ole Factory Rep (not Subaru)