Now you're injecting stability into the discussion and we induce another set of parameters all with various factors. The farther the CG is displaced aft of the Center of lift the less stable the airplane is about the lateral axis. We get into all kinds of fun and games there.
If an airplane is in level flight and all forces are equaled out so that all is straight and level and the airplane is in trim -- that is, no net moment acting to rotate it -- and the power is reduced, the speed will also reduce as thrust no longer equals drag, as speed reduces, lift no longer equals gravity, the downforce of the elevator is reduced, lessening the load-factor on the wing, therefore the airplane enters a dive seeking the trimmed airspeed. If it is truly stable and truly in trim (almost never totally) it will establish a glide at the speed it was holding in level flight.

You can demonstrate this with a high wing RC Trainer trimmed for hands-off straight and level with an engine using about 3-4* downthrust. Mine (I keep one for newbies) will enter a glide with practically nothing but reducing throttle to about 50%. Establishing the turn to final will require a small amount of back pressure, as will full idle on final. All glide altitude corrections require only short throttle bursts. In the approach and landing phase, elevator is used for speed control and the throttle is used for altitude control.

I use to love to see how well I could trim my flying machines. Some could get squirrely rather soon. An airliner was very touchy with just a stew walking back and forth. Big thing when you turn off the seat belt and all head for the potties at the same time.