Which factor does NOT influence the join-up of a formation?

The core of the question pertains to the factors that influence the join-up of a formation. The choice stating that a specific altitude assignment does not influence the join-up is accurate because join-up procedures are typically determined by the pilots and the overall formation management, rather than by a predetermined altitude.

When joining up, pilots aim to achieve a level of situational awareness that allows them to operate cohesively as a unit. Factors such as pilots' agreement on the join-up procedure, visual contact between pilots for spatial awareness, and requests among pilots wanting to join the formation are all crucial elements. These aspects ensure that the formation is cohesive and operates smoothly. However, a specific altitude assignment is not inherently necessary for the join-up since the formation can adjust its vertical position as needed once the pilots are in contact with each other.

Thus, the focus on mutual understanding and communication among pilots, rather than rigid altitude restrictions, highlights why that specific factor does not play a significant role in the join-up process.