Just for Clarical Purposes-
The way ditto works is this:
All HP Adders (such as Espeon) are applied on the defending pokemon.
Ditto copies the HP of the defending pokemon.
All HP Adders (such as Snowpoint Temple) are applied on Ditto.
If Ditto were to copy Magmar MT, it would have 70 HP. If Snowpoint Temple came into play, 20 HP would be added to Magmar's HP (making it 90). Ditto would then copy the 90 HP, and then have 20 Added to it's own HP (making it 110).