The "Width" setting adjust the front furrow only and causes the plough to pull "into" the unploughed work or "away" by pushing the rear landslide up hard against the furrow wall. It will only need a slight adjustment to get the correct front furrow width, if the front furrow slice looks high it needs adjusting "away" but if it is low then the opposite is needed.
A lot depends on your wheel settings and where the plough is set on the cross shaft. I tend to use 56" centres with that plough on Dotty but Henrietta has wheels set at 60" but both work well. If you measure from the side of your plough point to the inside wall of your tyre that will be your front furrow width and you can slide the plough a little on the cross shaft and use the width setting to fine tune. Do not forget to also use the leveling handle on the tractor linkage for helping to get penetration for your initial furrow. If you crank it up and get the plough to lean over onto the depth wheel, then crank that up, the plough will go in to cut the first furrow. If it does not then you should stop and wait for a little rain.

Once into work then wind the levelling crank to get the share running level on the furrow bottom.
As Dave says, when you get the plough right you will know, the check chains will be slack, the top link will run in the centre and you will be able to take your hands off the steering wheel and not deviate from the furrow.
Think its "snobbishness" as to why people do not like EPIC bodies. They bury the weeds and leave a nice furrow to work with afterwards. The "ploughmen" prefer "YL" bodies but these only work down to around 4" and, on wet land, tend to smear the land over because of the twisting action of the body. I much prefer the EPIC myself.
The PM plough was painted light blue not E27N Blue as far as I am aware. I have never seen a dark blue one and most of the picture seem to show them in the light blue. My own came in light blue and had not been painted since leaving the factory and two I saw at the Woods Bros. Museum in Rupanyup were also light blue. Ransomes were painting their ploughs light blue before Ford painted the tractors that colour and it is very close to Empire Blue. Strangely the EPJ's, the later plough, appeared in E27N Blue.
I shall be meeting Anthony Clare who wrote the Ransomes "bible". We have been in discussion about a proposed book on J.J.Wright and Sons Ltd and he will be coming p to meet with us in January
Just a point, the PM plough is not a true Ransomes it was possibly based on a plough designed by Sherman, it uses Ransomes bodies but castings were made by Ford at the Leamington Spar plough works as well as by Ransomes in Ipswich