The allocations process in Projects can be done by the Budget values. Budget values are created by adding non stock items to the project task.
The allocation process will take the % completion value for the task (based on the items) and determine the value of the entry.
When you have a number of items on a task the chance is that they will each have different revenue codes. So you would want the allocation process to post revenue to each of those accounts and not have it set to one account determined in the process as it is now.