The phrase "are most efficient when" is correct and usable in written English.
You can use it to describe conditions or situations under which something operates at its highest level of efficiency.
Example: "These machines are most efficient when operated at full capacity."
Alternatives: "function best when" or "perform optimally when".
We are most efficient when we answer email in bulk at our computers.
Such systems are most efficient when their height is 30 metres (98 feet) or less.
Assembly lines with specialized equipment, for example, are most efficient when run at one speed and cannot be slowed down or run intermittently without severe economic losses.
This is because the diesel engines and gas turbines commonly used to power ships are most efficient when buzzing away constantly at close to their maximum output.
They also agree that stimulus measures are most efficient when aimed at low-income or middle-income people, because they are more likely than affluent people to spend any extra money rather than save it.
Markets are most efficient when both buyers and sellers exist, when products or services are discrete so that the exchange can be one-time, when information about a product or service (such as its technology or means of evaluation) is broadly understood, and when there are enforced penalties for cheating.
An alternative is to learn them automatically from experience, which is most efficient when there is a human teacher.
TNSA is most efficient when the target rear surface is unheated; otherwise plasma expansion partially shields the surface electrostatic field18,19.
Early detection of BCR is important because salvage radiation therapy (RT) is most efficient when given shortly after BCR5.
A value chain is most efficient when there are fewer transactions between producers and their final customers.
The suppression of fines is most efficient when a CSTR flow pattern is approached in the bed.
