IPE settles were indeed a joke.  (I used to sit at the elbows of a couple of the bigger players on Brent) But I wouldn't be sure they were always manipulated the same direction such that they would constantly hurt a 100% same side hedger.  If your analysis is in print somewhere I'd love to read it.

The locals actually called it "grab a grand" because the big boys were quite happy to give away $50k on the settlement to them because they made ten times that on derivatives or physicals priced against it.

very very accurate.  Also done extensively with Platts/Argus based derivatives.  I could tell you some interesting things but I'm not sure about the statue of limitations.

Again, all the "real" players have to do is fix their own prices a significant percentage of the time.  It's the abdication of pricing to a market settle or a journalist that shafts them (in my opinion).  There's no gun held to Statoil's head forcing them to price off of settles.  Just sell on an EFP and sell the futures rateably or when they feel lucky.  

It will be interesting to see if you can structure a more honest market.  The problems I see though are:

1)  Top brass fear corruption.  The like forcing their people to sell off of some marker system to avoid the ease of shaving a cent off a fixed price sale and have it re-appear in cash down the pub.  And the peons like it because they can pretend to be traders while arguing over the last cent or so relative to Brent, when in reality their job isn't that hard or stressful.

Top brass also fears accountability.  If their team can't match the settle, the stock holders have a legitimate right to ask "why not sack all of you and just term up the sales to XYZ trading house".

2.  Oilco and consumer company traders are just not well trained or up to the task much of the time.  The ones that get it move to the Wall Streeters or traders.  It's hard to win in a game where your team is 3rd rate.

3. Oilcos and consumer companies not are always that honest either.  For example, Oilcos have no qualms about shipping surplus materials out of their markets at a loss to prop up the price of the local mkt.  Consumers will try to keep high price purchases secret to avoid affecting their floating priced purchases.

As for direct collusion re marching prices up and down, I never saw that between majors and Wall Streeters (I worked for both).  But I'm 10 yrs+ gone and wouldn't doubt it much from one oil particular major or the  crude traders at one particular IBank back in my day.  The same players are still around today, just at different desks..  

I had Dutch trading house traders ask me out to lunch and suggest precisely that sort of tactic and carving up markets to keep aquisition costs down.  The voice brokers would hint that party A and party B were undoing their published deals in secret, but they liked the money too so you could never get them on record.  European markets were a real swamp.  There was no honest business with ENEL before 1995 and the revelations re Elf were no surprise.  IIRC, the German govt owned a piece of one of their sleazier trading houses.  When the regulator's political parties are part of the scam, it's hard to get an honest playing field.

The collusion on cutting brokerage commissions was real as well.  Some of those guys are lucky not to have seen the inside of courtrooms instead of just getting fired and participating in a manpower shuffle with higher salaries at the end of the day.