Thanks for putting up that link Johnboy.
I couldn't find one at the time, but the pictures illustrate rather well how the modern convex fluke is not really a plow at all, but if it's holding power is exceeded, the shape, (adopting Nomad Will/Erics aircraft analogy here - thinking of holding it at eye level and imagining it being forced through a medium), will tend to sustain a downward thrust, but as it slides through the substrate slowly, it can shed the compacted substrate as it moves, thus giving a controlled drag, usually without breaking out.
Whereas those with concave flukes, while maybe having a higher absolute holding power when well-set and not moving, if their holding power is overcome, they will more likely tend to fill the fluke with compacted substrate as they drag, and even pop right up and out, as any downward force would be negated by the bottom-filled fluke.
That's my take on the difference anyway, and Steve's tests tended to support that, and I suspect why the Sarca Excel came out number one in his series, even though it may not have quite as high ultimate holding power as say the Spade or Rocna Vulcan.