Just in case we manage to sail there this year, Malcolm Mackley has done a couple of articles for Yachts & Yachting about where to go (and not go!) in Salcombe against the tide which I found today.  Though the one on the beat to Blackstone gives 3 options, all of which I have tried and all of which haven't worked!  Anyway, here's the link.  I suspect the answer is that there is only one place on the line to get a decent start and your short-tacking technique has to be absolutely flawless.
 yachtsandyachting.com/news/228062/Fast-Track-Sailing-in-the-Salcombe-Estuary-part-1

When you get to Biddleshead then it really is a gamble as to when the best time is to head out and find an eddy as you approach the mark, found it a couple of years ago when everyone was struggling around the rocks and I found a great eddy to take me to the mark and away from 30+ boats rafted up at Biddleshead.

Well done Malcolm, and thanks Andrew for drawing our attention to this.
It really reminds me of what we are missing - I do hope I can get to play these games again. 

While perusing the Y&Y site after reading Malcolm's 2nd piece I found this wonderful piece by Graham Cranford-Smith. So apt. Thanks for the amusement.
https://www.yachtsandyachting.com/news/228027/A-Letter-from-Salcombe 

Malcolm’s advice is sound and based upon years of research in looking at all of the other options!
 
However with 60 boats on the line, the game is all about clear air and rank at the start until the fleet has spread out.
 
On a South Westerly experience suggests that winning the beach side is essential whereas as long as there is centreboard depth on the Town side, a slightly less than perfect start can be got away with.
 
Malcolm doesn’t mention the need to be absolutely as close as you can to Woodcot Rocks before crossing to Biddle, but maybe he was keeping that to himself!
There is a really good case for doing a bit of a beat from both sides to the Blackstone mark before the start to get an idea of the true wind direction and which side is lifting.
We missed you all at the weekend.