We're trying to install a Radian (xtsl) FF in the center of a 2005 Town and Country. My husband did the initial install with the seat belt and rear teather and I assumed it was an ok installation...later, I noticed the shoulder straps on my son weren't tight enough and yanked on the tightening webbing (which is reeeeallly stiff) and the entire seat bottom moved forward probably 6 inches. We just tried it with the off-center latch instead of the seatbelt...same thing happens--lots of movement there. Is this normal???