Advice with structuring CA contracts

Generally you may be limited by the way agencies structure compensation. Technically, they are not allowed to negotiate taxable and tax free compensation, but pay all travelers in the same area the same stipends. Some do negotiate stipends, and that is fine from a traveler perspective. Just saying that if you are going to use agencies new to you, your negotiation ability may be constrained in this regard compared to your current agencies.

Overtime after 8 is a complex issue. Not all agencies, or specifically not all contracts will pay overtime after 8. Hospital units may vote on an alternative work week, and if they have one in place, the agency is free to pay 12 hours straight pay. Ultimately it doesn't matter as all an agency has to do is make the effective, or "blended" rate the same by lowering the base rate, paying overtime after 8, with the same total hourly number. Thus some agencies, especially CA based agencies or agencies tired of travelers telling them they must pay OT after 8, will always pay time and a half after 8.

No matter how they quote, you are looking for certain things to be true. What matters is your total pay (use PanTravelers calculator), maximizing stipends inside that total pay as much as possible, and negotiating overtime rates separately as you have been doing.

Some agencies will continue to base OT rates on that relatively low base rate, yet provide a shift bonus for overtime to bring the rate to a reasonable level. Emerald does this for example (a large CA based agency with lots of CA assignments). That will still leave orphaned time at a lower rate for extra time on a scheduled shift. Not too much you can do about that except choose a different agency to work with if you are concerned about those few dollars lost.

Sounds like you are doing a great job with contracts!