I suspect you know that this is all a bit misleading.
Using the
link @Bigdwoolly provided shows the predicted points based on xG and has the top 6 in order as Derby (2nd), Pompey (1st), Peterborough (4th), Bolton (3rd), Stevenage (8th with game in hand) and Lincoln (7th). Pretty accurate.
Current top 6 and their over/underperformance in terms of goals scored
Pompey down 3 goals, around 5% underperformance
Derby up 7 goals, around 10% overperformance
Bolton up 10 goals, around 20% overperformance
Peterborough up 4 goals, around 5% overperformance
Barnsley up 12 goals, just over 20% overperformance
Us up 12 goals, just under 25% overperformance
As ever there is context to apply, it doesn't count chances where someone has missed a ball fizzed across the box or takes a touch instead of hitting it first time like Murphy at the weekend. Once a team is leading there's less incentive to go forwards and push for more goals etc but as it's not an awful system and the fact that it's quite accurate backs this up. As you say, the better teams with better forwards (and I don't remember you being particularly impressed with Harris under Manning) will tend to outperform and the lower teams with lesser players will tend to underperform a little, the biggest overperformers in the league are us, Barnsley and Bolton. You also say about Lincoln tailing off and yes, I think they will. They won't keep scoring about 80% of their shots on target while opponents miss one on ones and fall over taking penalties.
Taking it up to the point Manning left we were overperforming our xG by just over 60%. Plenty of people were saying it wasn't sustainable at the time but were often shouted down by people saying we were third highest scorers in the league. I certainly said myself I didn't think it would last and I wasn't alone in this.
This isn't a dig at Manning either nor saying he did a bad job or it was all luck. Clearly he did a good job here and not even his fiercest critics could suggest we didn't have a clear gameplan and organisation to us and we'll never know what he would have done had he had another window (although in hindsight was his summer window
that good? Seems we're lumbered with McEachran and Thorniley a bit, Perkins was a disaster and we spent a fee on Woltman who is miles off it). It's a pretty safe bet we'd be doing better than now and firmly within the playoffs rather than looking to sneak 6th. However I felt at the time and now that he had almost everything go his way, sometimes you make your own luck and you need to put yourself in position to take advantage but I think it's incredibly naive to suggest that we'd have carried on picking up results at exactly the same pace as before.