It is exactly the same regardless of EQ level.
I'll go one step further and say that if a wall is at 60% HP then EQ will do 20% damage (leaving wall at 40% HP) regardless of EQ level.
In fact, most of the time EQ behave the same regardless of spell level. The damage stat on description applies only for first EQ spell used on a fresh building.
The second EQ spell used on a wall does reduced damage and all spell levels become identical. On other buildings the fifth EQ spell becomes identical for all spell levels.







