Soft Halyard or Line Shackle

[Brion Toss]

Hello,
Great fun. This is similar to the work of rigger Matthew Otto, though he uses a series of locked Brummels. As for relative strengths, first quibble: I believe Lash-It has an average break of 500lbs.
Next, your pictures appear to show the line doubled on the scale, or nearly so (slight angle). If so, the scale will read about twice the load on the rope. Did you take this into account?
Next, there is no question that the Diamond weakens the rope severely. On the other hand the material is doubled in this configuration. Still it is intriguing that the attached eye piece broke. One question: what do you mean by an adjustable eye? I can't picture it, or how a whipping is involved.
With a clearer idea of the configuration we could conduct more formal tests.
Fair leads,
Brion Toss