How system is distributing WO operations within multiple resource units in Production schedule?

Summary:

We are seeing that Production Schedule is distributing parallel work order operations between resource units by it's own when there are multiple resource units available for same resource. Would like to understand the logic behind this distribution.

Content (please ensure you mask any confidential information):

Manufacturing scheduled resource has multiple units available in a Plant. Multiple work order operations are utilizing the resource units. When Production schedule is generating the schedule, it is distributing the work order operations between the available resource units and that is visible in Gant chart. How system is deciding which resource unit to be assigned to which work order operation to generate the schedule