Terms like "128x" in PTZs refer to the zoom factor, not the dynamic range of the image; there is ZERO correlation between the two terms.
At 128x they're probably including digital zoom. A "typical" optical zoom might be something like 20X, which could indicate a lens that ranges between 3mm and 60mm, or from 6mm to 120mm - strictly a ratio of longest to shortest focal length.
Some manufacturers will state their WDR is 128x. Meaning the different between the dark and light areas are 128x compared to a "conventional camera".
"Panasonic Super Dynamic III technology delivers 128x (NTSC) wider dynamic range compared to conventional cameras." https://security.panasonic.com/pss/security/products/pdf/WV-CW970CW960_2A-012CA.pdf
This is falling out of favor, because it is hard to measure vs. a dB rating. Also, the next manufacturer can then make a camera that delivers 129x WDR and is "better performance".
It shouldn't have anything to do with PTZ vs fixed cameras. Just how some manufacturers state their WDR performance.
In general, WDR ratings should be taken with a grain of salt, as they are self-assigned, whether it is measured in dBs or 'x's.
I am curious to know: what is the purpose of finding any correlations between both, if any ??? Just for mere personal intelectual curiosity or are you having an actual real project challenge ??
"Measuring how well a camera handles dynamic ranges in a scene is difficult, and the units typically used on product datasheets (such as dB) are NOT a reliable indication of actual WDR performance." to quote what "X" famous manufacturer is explaining in one of its whitepapers.