Why does bass have more “punch” when I stand up vs. sitting?


I have Rockport Avior speakers and I notice when I stand up the bass is slightly louder and has a little more punch than when I am sitting. This is with the same distance from the speakers. And the speakers are level with the floor. I do like the sound more when standing.  Has anyone experienced this?  Suggestions as to how to have the bass response while sitting as I do when standing?  
lourdes
The rugs should be between you and the speakers; first reflection point is an imaginary straight line from the woofers hitting the floor, then an equidistant straight line to your ears on the couch. Also, the ceiling above that area is a reflection point.

Try putting a big thick duvet down to see if it helps.
What happens to the high frequencies when you stand up? If they don't change maybe you could consider raising your seating position instead of the heavy speakers.