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+1 @ above, i.e. 80mm = 80mm
If you are familiar with an enlarger in the darkroom ... think of it as though you were projecting an image onto an 8x10 piece of paper. Then without changing the height (akin to FL) of the enlarger, you switch out the 8x10 for a 4x5 sheet of paper (akin to smaller sensor). Your projection will have not changed at all, but you will only be capturing a CROPPED portion of that image projection. Then if you switched out the 4x5 paper for an 2x2-1/2 (akin to even smaller sensor), it would be an even further CROPPED capture of the projection.
So without making a change to the enlarger height, when you present the prints captured by 8x10, 4x5 and 2x2-1/2 papers side by side, each one will display a different amount of the image that was projected, but they will be identical for the corresponding areas captured. Hack the 8x10 down to the size of the 4x5, identical. Hack them both down to 2x2-1/2 and all three will now be identical. The cropping is only going to indicate how much of the projection you are throwing away ... i.e. nothing is really getting "multiplied" just because you capture a smaller area of the projection.
The one thing that is definitely different about using MF glass is that the projection is spread over a larger area (image circle). This makes for smoother transitions and reduced vignetting, particularly when only the more centralized (straighter rays) portions of the projection are being captured by the sensor. When I mentally separate the projection (lens) from the capture (sensor/paper) it is much easier for me to understand that 80mm = 80mm. Which body I put on behind that projection will dictate how much of the projection I have captured/cropped from it ... i.e. crop factor.
Whether that is on my FF (1X) or my 1.25X or my 1.5X cropped sensor. It is just telling me how much of my projection I'm NOT capturing RELATIVE to FF.
But for ease of mind/practical use ... 80mm = 80mm.