Minimum length of mini-split AC line
The manual for the Pioneer mini split system I'm installing this weekend says the unit is pre-charged for 16 foot lines. For distances less than 25 feet the manual  says no change to the refrigerant charge is needed. Nowhere that I can find does it say the pipes have a minimum length.  

Maybe see if the installation manuals are available on the Internet for the unit you intend to purchase. They should have similar guidelines.