When an almost single-mode IR laser beam is reflected from an IR window with a deposit of Rydberg Matter on the inner, vacuum face, the laser modes appear red-shifted; thus their maxima are observed at lower laser current. This effect is complementary to the previously reported blue-shifts of IR laser modes in transmission through Rydberg Matter. Both types of shifts are due to interaction between the laser modes, now proved by using only two isolated modes both in reflection and transmission. The general process is stimulated Raman scattering. Rydberg Matter is here formed from Rydberg states of K atoms and nitrogen molecules inside a vacuum chamber. A theoretical description is given that involves slow decay or increase in the energy of the photons interacting with the Rydberg Matter, depending on the temperature of this matter. This means that the two isolated modes studied may become almost resonant within certain frequency ranges. The energy increase (frequency blue-shifting) of photons passing hot Rydberg Matter has been reported previously. The description used explains both the red-shifted reflection and the blue-shifted transmission results.