Mares Morphos Twin

I have a question regarding the shoulder strap holders on the Morphos Twin.
The manual doesn't cover this for some reason.

Both shoulder straps come back into a piece that is looped into the
backplate and two pins lock the loop in place. There are two pairs of loops,
which allows the attachment to be raised or lowered, obviously affecting the
fit and height of the backplate on the back.
We just got two Morphos Twins here, one in large and one medium. Apart from
the M and L labels, the piece of webbing joining the two shoulder straps
also has roman number labels showing a "I" on one of the BCs and a "II" on
the other.

Is this all just a matter of personal ajustment according to prefence or is
there more to it?

Cheers,

Marcus