G'day MD.
IIRC, that pack is essentially a lumbar pack on a reasonable belt, and the "strapettes" are accessory L & R shoulder straps ? I don't remember how high above the waist belt that the top of the bag is, which may affect my thoughts below.
I have a Kifaru Tail Gunner which is also a large lumbar pack, for which I have accessory shoulder straps.
If you check in Google Images you will find pics of the Kifaru TG, showing the attachment points for these straps. The pics also show short straps angling from the top inner corners of the bag down to the belt. The bag also has compressions straps.
After using the shoulder straps for a while, I discovered that if I used the compression straps, and the short straps angling down to the belt, I could hold the bag in close with minimal sagging and dragging. Can't say what loads have been in it with the shoulder straps, but nowadays I would guess maybe 3.5 kg gross. It has been heavier (when I was younger

)
That is the way I now use the pack, and have not used the shoulder straps for many years. I would be inclined toward seeing what you can do along these lines before mucking around with shoulder straps.
Add : There are differing iterations of the TG shown on Googleimages. The following two links show the one that I have :-
https://www.rokslide.com/forums/threads ... lt.157688/https://www.worthpoint.com/worthopedia/ ... -482424986