It's not the points difference which makes me think you won't finish 4th its that my opinion is that Liverpool simply aren't as good as Arsenal or Chelsea and finishing ahead of two teams that always finish in the top 4 is unlikely (as it is it seems one of them won't finish top 4 due to Spurs, very unlikely IMO for them both to miss out)
I said it before if it was between Liverpool, Arsenal and Chelsea for 3rd and 4th things would be different but its not, it's all 3 teams fighting for one spot. You all but said it yourself you need a second half collapse by Spurs which at this point looks unlikely....
Personally think your logic is wrong here
I would go along with this if it was August, and no one would expect (or dream) that Spurs would be flying so high with nigh on 1/2 the season gone, so your point that its very unlikely that both Arsenal and Chelsea would both miss out (esp given Chelsea's strengthening over the summer) would hold true.
The logic, imo, breaks down once we "know" (or is fair to presume) that Spurs are more than likely to take one of the spots - so the odds fall drastically that the two other london clubs will fail , and imo the odds fall further because all three clubs are so close points wise after 18 games.
Its by no means definite that Liverpool will get the last CL place, of course not, and if you had Arsenal's attack (esp RVP) with Liverpool's defence, they would probably be giving the Manchester clubs a run for their money (thank god that isnt happening lol).
Its fair to say within a not too surprising single weekend they could easily be completely level on points (and yes, just as unsurprisingly , there could also be a 6 point difference with Arsenal "top")
After the jan window closes (because no one knows how much Chelsea and Liverpool are going to spend ) without major spending happening I would put money on the gap between all three clubs being similar to what it is now in May
