the rule seems like...

oops,
although the rules seems perfect,
after I done more analysis, it seems broke.

when I increase the error to 3A,
although I can hit all the 4 pair strands,
I also hit sandwich.

you'll hit sandwich when error's about 2A.

it seems like it will try to hit a sheet more then four strands.

but the question is, why the "bend" appears the way as my rule?