It really does not matter what length the arms are. You will be installing a system that comes with all the parts. Do not try to mix parts from different brands! The instructions will tell you where to mount the trailer tongue parts for the system to work correctly. I would not deviate more than the stated tolerances in the instructions. Engineers have worked out all the details for the systems. Believe them. Again, you are getting a SYSTEM that comes complete. If a company offers systems with different length arms there is probably a reason for that. This is not the place for experiments. Call the company that makes the one you are interested in and tell them about your setup and ask for their suggestion.