Last Mile and Private Last Mile tests can be set up as Single Orders (which run independently) or as Batch Orders. Batch Orders ensure that the tests run through the same machine sequentially for more comparable data.
You must have at least two tests in a Batch Order. A Batch Order can contain a maximum of 6 single-URL tests or 3 multi-step scripts. This is not an adjustable setting.
For more details, see Creating Batch Orders in the documentation.