Refactor Overwriting Combinations in Matrix

[EmmaMunley]

Changes

This commit refactors the overwriting combinations function within fanning out the Matrix to reduce the number of calls in the call chain as requested by Priti in PR: #6341.

/kind cleanup

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Release Notes

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[EmmaMunley]

/assign @pritidesai
cc: @jerop

[JeromeJu]

Thanks @EmmaMunley

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This pull-request has been approved by: JeromeJu, jerop

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[Yongxuanzhang]

/lgtm