How come it's easier for me to reach my back with my left hand (for example, to scratch a rather inaccessible area) than with my right hand?

I find that when I try to reach the middle or upper half of my back, to scratch an area, it’s easier to use my left hand and arm than it is to use my right hand and arm. When I reach with my right arm, I have to strain, and I find it tight and restrained. However, when I use my left arm, it has little problem reaching the area. Is it because I’m more flexible on my left side? Or is my left arm longer? Or both?