Is this something you have tested and prove
No sir; i'm sorry this is simply what i've always seen handling it and making sense out of lessons handed down.
This is why i didn't reply at first here or other places.
i always thought and felt, of course 'Leftie' isn't as secure;
it mechanically can't be.
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Sheet Bend doesn't have the Nipping Loop - pulled from what would be the eye side
BUT, same loop would be pulled from it's S_Part;
but any way it doesn't seem to be the side trying to walk off the job;
As it forms a Hitch, it's Bitter End is sitting on one of the hardest surfaces to Nip proper.
Bight side seems the escape side, not forming a Hitch lock/ not crossing turn nipped by self.
.
To me, they are visually similar, forces do run different loading patterns ;
but still just as the look similar, each has an escape side, and a lock side;
and depends on line tension and hard surfaces as Nipping tools, like any other.
.
So i think, to Nip against the hardest surface, Bitter End of escape/Bight side
must follow into hardest S_Part line
As GREEN Bitter End seats to BLUE S_Part
But, PURPLE Bitter End evades this hardest Nip, by turning away from it.
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Orange side of eye forms a Hitch on own,
Green side of eye forms Bight w/o hitch, so is focus of trying to 'nail down'.
My eye simply doesn't expect as much Nip on leftie, tried to reveal this with the colors.