Thank you, gentlemen...much good advice here. It may well be that 'distance-to-camera' is the heart of my problem, seeing as my 'distance-to-monitor' is determined by the non-prescription glasses I use when sitting at the computer. I will cobble together a shelf and move it back. It has crossed my mind, in a general sense, that I should sit back farther as indicated in the tutorial diagrams. But in the heat of battle, how I sit is driven by the depth-of-field of my glasses; being non-prescription magnifiers, they're only in focus within a narrow range.
As far as ambient light goes...might be a contributing factor during the day, but definetly not at night, tho' reflections off glasses could. I'll search out a dulling spray at the hardware store. Thanks. TrackIR is much, much more sensitive than I thought. Sweat?
I haven't attempted to adjust the curves yet. First because it all seems to work so well during the set-up, and secondly, the tutorial was written for T4, and I have T5. Everything has changed and been moved around, so I'll go there as a last resort.