i think they usually come with a plastic h shaped block (maybe another brand battery tho). or just measure your height difference and cut wood or plastic and put it underneath battery...
I got a honeycombed plastic spacer from another type battery at Pep Boys (they always have extras or unused ones around).
It did need to be sanded down to properly space it under the Optima, then I used the stock hold down.
placing anything underneath it will rise over the stop blocks. something under the bracket is the solution unless you drill and mount something else to stop it at the bottom. i don't know....i'll come with something eventually a year later...lol.