$500 math question on extending ball mount shank

drsteve wrote:
According to eTrailer, a 12" extension reduces your tongue weight capacity and tow rating by 50%.

https://www.etrailer.com/search/Hitch+Extension

Second item down the list...

Op here, Thank you...So, every inch of extension I loose 4.17 percent.

I did read on-line (unknown if true or not) that hitch ratings are based upon... 10 inches back from hitch cross member at center mass. So the first 10 inches are free then after 10 inches subtract 4.17 percent for every inch.