The 2" riser has nothing to do with bed clearance, you can go without the riser and have 6" bed clearance but the RV WILL ride nose high. To get a minimum of 6" bed clearance and a fairly level RV the 2" riser WILL be needed!
Mine in pic is very nose high, risers will be added later next week. Pic is deceiving, RV is 3-4" higher in front than rear.