Yes, this is the commonly held belief with outdoors enthusiest. In the construction field, though, the radient barrier is put on the outside of the mass insulation. Because the insulation is still a thermal body radiating heat. The goal, for buildings anyway, is to keep the heat inside the insulation which is keeping the heat in the building.
http://www.radiantbarrier.com/faq.htm
Because the IX is such low density and so thin. It is my belief that it will have no effect on the thermoflects radient ability. I doubt any significant difference in warmth would be noted in either configuration.
Now if a person where to use the blanket with a lower rate quilt for colder temps. It would be most effective to put the thermoflect blanket on the outside. As with construction standards this will keep the heat in the TQ longer.
If used inside the TQ, you would feel warmth almost immediately but in the long-term you would get cold, I think. This would be because your body isn't able to heat the actual insulation in the TQ fast enough. That's the theory anyway.