By what mechanism is girth gained from length only exercises?

After doing some reading and talking to forum members I’ve learned that doing length only exercises like manuals and traction will inadvertently add some girth. According to the wiki on r/ajelqforyou and personal accounts of PE’ers it seems that 1 inch of manual lengthening will add around 0.25” of girth and 1 inch of device lengthening will add around 0.15”. What I want to know is how is this happening? Obviously there’s some factors that increase or decrease girth gains from lengthening as seen with the difference between manual methods and devices.

Could it be that manual gripping methods like a hand or noose damage the layers of shaft tissue more than a something like a silicone sleeve or vacuum bell thus causing cell repair and growth along the shaft? That’s really the only thing I can think of.

Personally I want to find a way to lengthen without adding any girth because I’m already at 5.5 girth and it seems that’s about the limit for spontaneous sex, anal, and blowjobs. All I want is around an inch increase in length with no girth increase.

Summary: How exactly do lengthening stretches increase girth and how can I stop it from happening?