Original here.
When using the Spread arrangement, Custom First Spacing lets you control the location of the second rafter. After that the regular spacing is used, until the end, assuming End Rafter is on. By tweaking the first space distance, you should be able to 'balance' it with the end space so all the rafters are centered. Quantity parameters for the First and Last rafters allow you to have multiple rafters of those special lengths. For example, exposed rafters in a deep gable end, where the overhang is greater than the rafter spacing. There are Top End parameters for the first and last rafters, so they can differ from the main rafters. Use the Match setting to keep the ends the same.