For true cinema lenses with a stated T-rating, the T-stop is generally meant to represent total transmitted light through the lens, not just glass/coating losses. In practice, that means it can reflect the lens’s overall light transmission as measured across the image formed by the lens, rather than promising equal brightness at the center or edges.

So: two lenses with the same T-stop can still have different vignetting patterns. The rating means the total light transmitted is comparable, not that illumination is uniform across the frame.

T-stop itself is not tied to sensor size; it’s a property of the lens. But the visible effect of vignetting does depend on how much of the image circle your sensor uses.

For third-party measurements, such as lab-derived transmission figures, whether vignetting is included depends on the measurement method.

As for stopping down, you generally should not assume a fixed offset from f-stop to T-stop at every aperture. For ordinary still-photo lenses, transmission can vary with lens design and aperture, so the relationship is more complex than simply adding 0.3 everywhere.