When assigning equipment, AutoStow does not assign a specific RTG to a specific quay crane. To feed a crane with just a single RTG, the productivity of the RTG must be equal to or slightly higher than the crane productivity. If an RTG's productivity cannot follow the crane's, AutoStow uses a second RTG to prevent crane delays and may even consider using additional RTGs up to the value you set in the "Total number of RTGs available for the load" configuration.
After AutoStow picks the first container in the work queue, it "tracks" subsequent RTG positions by scheduled move time and location. When choosing the next candidate, it tries to minimize crane delays and clashes. Before moving an RTG, it computes how long the move will take and whether it will incur a delay. Depending upon parameter settings, an RTG can easily move a few rows and still feed the crane in time. However, if selection of that RTG causes a crane delay, XPS selects another RTG.
Forklifts use the RTG set of penalties; however, extra travel time is added to allow the forks to switch from one side of the block to the other. Using the parameter CFGFTL (on page 1), you can specify the total number of front-loading type CHEs available for servicing a vessel. If CFGFTL is set to 0, AutoStow selects an RTG to work in a forklift block.