It's not whether the wheel is over the line, but how much of the car length. Yours looks about 25% over, although there's no photo taken from the side. However, this is over any de minimis consideration with the rear wheels by the double-yellow lines. So you can't really argue the PCN.
Is the tow disproportionate ? Well, you're into double-yellow lines which mean No Waiting 24x7, so it would be difficult to make this argument. But you've now paid all there is to pay, so it's a no-brainer to make them do some work for their ill-gotten gains and appeal this on disproportionate penalty. Of course the council will refuse your representations so you'd have to go to London Tribunals. If you lose, you've already paid anyway, if you win, you might get the tow and storage fees back, but I can't see an adjudicator agreeing to cancel the PCN.
Others may differ, so wait a bit, but don't miss any deadlines; you only have so many days to submit reps to the council.
Other things that can win are fatal errors in the PCN, and also incompetent practices in the car pound resulting in you not getting all the documents that you should be given.
