The complication comes through EPS. So, while fifth now gets you into the Champions League and sixth into the Europa League, for the purposes of competition qualification, the EPS situation doesn't count.
So, if Chelsea finish sixth and win the Conference League, without EPS, they would already be in the Conference League berth, so they go into the Europa League as Conference League winners and England would not take its Conference League place. With EPS added, instead of the sixth-placed team (Chelsea) qualifying for the Europa League through their league placing, because they are already in, the seventh-placed team benefits. So that would be three English teams in the Europa League and none in the Conference League.
By the same process, if Chelsea finish seventh and win the Conference League, without EPS, they would qualify for the Europa League despite being outside the European places, meaning three English teams in the Europa League – Chelsea, Palace and the fifth placed team – and one – the sixth-placed team – in the Conference League. With EPS added, everything drops down a place BUT as Chelsea are already in the Europa League, instead of the Conference League spot going to them after finishing seventh, it goes to the eighth placed team.
So that implies that if Chelsea are 6th and we are 7th (i.e. draw on Sunday, Villa beat ManU, City get at least two points from their last two), we get a Europa place.
Which does go some way to resolving my question about Opta rating our chances of Europa so high vs conference, because that moves a reasonable scenario into EL qualification when I'd assumed it was a conference qualification.