I don't know how large handheld stacks are successfully achieved either! I would think it easiest lying down, using a camera with a viewfinder, with your elbows on the ground. With the K-01, because of no viewfinder, the camera is, I think, quite a bit less stable, which makes the fine control needed for stacking harder. The reverse advantage is that I can reach spots where it would be impossible to put my head.
I also tend to think that because my body stays a bit further out, it's less intimidating for critters. Another consideration is that I've mostly used the onboard flash (with homemade diffuser), which lightens the backpack considerably but also makes it harder to fire bursts of shots - possibly another stacking trick. (The onboard flash often takes 3-4 seconds to recharge.) I'll be switching to off-camera flash soon and might try that with a monopod...
TER-OR, thanks for the tip about early morning shooting! Not sure I can get myself out there super early, but it's good to know.
This shot was fired in the late afternoon, around 5pm. That individual was super calm, and there was no wind.