I have ran into this many times to the best way for a customer to under stand it is to put it in simple terms.
Everyone should lay it out up front to the customer that you should not OK them to use less than what is speced. They should have received the VM deployment guide and it has exactly what is needed.
Would you drive your car around with half of the air in the tire. Yes it would work for awhile but when you really need it, its going to fail.