I've used Caustic at 85C without problem, and I'm not aware of any limiting factor up to boiling, though above 85C there is a lot of steam to contend with which can lead to changes in concentration over a period of time.
Most detergents have other chemicals blended in- surfacants wetting agents etc, These may have different propoerties to the caustic base, but I'm sure your chemical supplier can probably provide any info on limitations for your specific blend.
We tend not to drop below 1% purely from experience, a few years ago We'd typically use 2%, but as chemical blends have improved along with the design of plant, we've found that 1% blends provide a reasonable compromise of wash time against chemical cost. I do not recall any client wanting the level reduced further.
This level also still gives a reasonable conductivity difference to monitor when sensing changes from water / detergent on automatic systems or for automatic dosing systems.
It's all down to setting a system up that is repeatable. if you can acheive the wash standard you need at a low concentration, you simply don't need more chemical. If the chemical strength is limited you can increase time of wash, but in most cases the down-time is more costly than the chemical.