Originally I played with sdf space kl; but I noticed my left hand had substantially better stamina than my right. When I started looking at the physical positioning of my fingers, I realized that my left wrist tends to rest farther away from the keyboard, and my fingers were straighter than on my right hand. This was because my right wrist needs to be closer to the keyboard for my thumb to hit the space bar correctly. So I decided to experiment, and moved my right hand up, creating more space between the space bar and my fingers. After a short adjustment period, I saw a noticeable increase in my right hand's stamina, so I decided that this positioning seems to work better for me.
So I'd say it's probably one of those player specific technique related things.