<font color="blue"> The top of the root ball is aprox 8" below ground level on the high side of the slope. </font>
I would set the top of the root ball at the same level as the high side, which will then be slightly above on the low side after you backfill. You can always add mulch, etc. to the lowside -- as you have it now, you are going to be burying the top of the rootball, which is not what you want to do.