We've seen this location before a few years ago, but I can't remember how it turned out. The restriction signs cannot be seen until one is on top of them due to the sharp bend and the tree and hedge obscuring the signs until the last couple of seconds.
It's a pity you didn't come on this forum before submitting your representations, because you could have put in a lot more than just base your case on one adjudication at London Tribunals. May I ask if you submitted reps for each PCN or if you submitted a single rep plus a list of the PCNs. I'm assuming you got the first PCN after some days had passed and in the interim, went the same way unaware of the contravention. Cases like this can be argued that the subsequent PCNs dated before the first one arrived in the post so they should be cancelled.
Other point to be aware of is a recent London Tribunals case where the council argued the blue advance signs gave notice of a restriction, but this was shot dowe y the adjudicator on the basis that they are not traffic signs, and the TSRGD has signs in it that the council could have used. It is on this forum somewhere but I cant' remember the location, sorry.
Anyway, the real question is - are you prepared to take them to London Tribunal, with the full £160 in play ? If not then you might as well pay-up now at the discounted £80. You have a reasonable case, but it isn't a "slam-dunk" win so you might lose.