As a concerned  owner and user for one of these systems, I would like to say no to changing the design.  We had this done at our home in 2006.  Within months, we began having problems.  The company did come back and add additional area to our septic (which should have been there according to our permit) and we also paid to have that area installed.  Talk to your licensed professional before you agree to any changes by your contractor.  In our case, we were told that "these were the only systems being approved by the county". 

I feel we were mislead by the county health department and our contractor.  No one told us what the impacts making the septic design smaller would do and that it was the at the discretion of the contractor.  How could the person responsible for the design not be able to stop this?