Its obvious it has been modified between the black & green section (rusty section). I'd bet it was not correctly measured/cut/welded..... I have a C-pillar hoop I could get some measurements on for you over the weekend if you wanted to remove yours and compare.
I doubt anyone would notice if you shortened it to make the lower edge of the soft top line up with the tub properly.
You are also missing the tub rail holder for that rear hoop:
65852-60011 1969-1984 40 series Soft Top Corner Rear Bow 'Stopper' Brackets
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