Another factor that hasn't been discussed here is the wind gradient factor. The wind are faster at higher altitude and slow as you descent. Judging airspeed isn't really practical by just looking at how fast the plane is moving is relation with the winds at ground level.

I have flown full scale for 45 years and also fly sailplanes. You have to add a percentage of indicated airspeed to your approach speed as you make turns during your approaches. With those long wings, the lower wing, during a turn may be in significant slower relative airspeed than the upper wing is. You can stall the lower wing even though your indicated airspeed is shows you are above stall speed.

While it is not as noticeable with our models (because we fly at lower altitudes) it is still a factor, especially with higher wind speeds, not to mention gusts.

I have found that judging angles of attack is fairly easy by simply looking at the wings. If you see the top of the wing during approach.... go get the shovel. If you see the bottom of the wing, then you are in a nose high attitude. By learning to look at the wing and judging the angle of attack by the width of the area you see, you can accurately judge your airspeed. Since angle of attack determines stall speed, knowing what angle your plane is at, allows you to use the elevator to control this angle allows you precise control during approach.

It works for me.

Rod