rear gate strut

I have a 2006 Chevy Trailblazer LS 2WD (S15506). The body-chamber of the OEM Lift-gate Strut measures 12.25" before adding the length of the chrome shaft. However, so far all "matching" after-market Lift-gate Struts, the body-chamber measures 13.25" before adding the length of the chrome...