Simes303, interesting to hear about your plumbing of the depth.
I agree with most of your topography of the lake bed, but are you certain you covered it all?
My own plumbing of it showed a deeper pocket, running roughly North to South South West. The pocket is probably 8 to 10 meters wide at the SSW end, and maybe 15 meters wide at the N end, which is where you should be seeing around the 50 feet mark.
Of course, I am happy to be corrected on this, you clearly know what you are doing, and my own research was done only from the bank using a long range marker rod, coupled with a decent casting reel, but I did spend a full day doing it. Will try and scan my hand drawn map in for you to look at.
One possible explanation is that at that distance, undertow created a large bow in my line, making depth appear greater than it actually is. I suppose the same phenomenon could have led to inaccurate mapping of the deeper pocket as well.
Whilst on the subject, has anyone fished it recently?