My two cents ~
It depends on the actual wording of the contract being worked on.
In LORT, it states that SM's and ASM's, in addition to their contractual salary, will be paid an additional 1/6 of contractual salary. HAT and Mid-Size say 2/8's of contractual in addition to contractual salary.
As always, call your local Equity office and ask the Business Rep who handles the contract you'll be working on.
And then - negotiate!