Dyneema fail at masthead sheave!

[MJohnson]

We are scrutinizing our reacher halyard after it parted at the mast sheave on our last passage.
Our furling reacher hoists on a 2:1 purchase to an Antal 90mm tulip sheave with a maximum recommended line diameter of 14mm. The functional diameter of the sheave is 66mm.
Does the recommended max line diameter indeed include cover and core? Our broken halyard actually measures 15mm, but the cover is somewhat loose over a 10mm Dynex Dux core.
Would it be an overall stronger system to use a 12mm overall halyard so the strain caused by bend around the sheave is reduced? Other possible combinations include using the core only or core with chafe cover only.
How much is strength compromised when the minimum recommended bending radius is disregarded?
If we extended the bury of our eyesplice to continue past the mast sheave, will the increased diameter and stiffness reduce our functional strength or possibly increase strength?
Thanks in advance
Martin