It is nuisance everywhere. My manager does not want to be in loop with the HR because signing post HR declining will be super-ceding HR on record and he does not want to do itIf you can add any email communication (to LOE) with HR refusing to list your job description because the standard form doesn't have it. Also, when you email them, cc your manager so that his email is shown. Then on the form that you would like your manager to sign, ask him to include his email so he match.
I will add organizational hierarchy for proof of he being my Manager. Though my offer letter also has his name as Reporting Manager