Not at all, I just shot these for this thread, I'll do some more once it has gone dark.
You're actually shooting clay heads :-> ... did you make them for practice? This is a great idea, I also wanted to do that but never came around to it, that's why I have to keep asking friends of mine to pose for paramount, loop & rembrandt lighting :-p
Fourth image is 1/250 all else the same, we now have eve more contrast as the face image left is another 1 1/2 stops under the face image right.
Hmmm, this is not my recent experience - in your shot, you've got a nice window with daylight and you're shooting at rather shallow dof with f2.8.
The day before yesterday I shot in a dimly lit room in the evening with a medium window - and I needed a larger dof and a fast shutter speed because I was doing a portrait of a friend of mine with her dog on her arm. I used the ambient from the window (I didn't measure it) as shadow fill for a flash from the other side as key light - and I was @iso1600 to see any noticeable ambient effect.
I calculate: darker ambient than in your example = maybe -2 ev ... smaller aperture = another -1 to -1.5 ev. ...and that's for a "flash type" shot, a more natural "ambient style" shot would even need a higher iso setting.
I'm definitely not through trying to mix ambient & flash indoors, so I'm open to other experiences :-) but I think the combination of deeper dof + dim ambient in non-studio situations makes quite a difference.