NHS Pensions - Annual Allowance Excess Charge and Scheme Pays - very complicated but how does b/f unused relief affect matters?

I don't think I am alone in finding the whole Annual Allowance Excess Charge and Scheme Pays rules (client has NHS pension scheme) absurdly complicated and the guidance unclear on Gov.uk (for example it does not highlight that the employer contribution for tapering is the 'pension input amount' rather than the 14% the employer pays into the scheme, which people I have spoken to thought).  

The rules also seem unfair because 'scheme pays' doesn't apply to the excess charge that arises as a result of the annual allowance tapering below £40K. The latter must surely have been a drafting oversight and not intentional?  Given the problems I have had with the calculations and the fact that NHS pensions are only sending out letters where the pension input is more than £40K and many will have to pay the charge on inputs between £10K and £40K and will not realise because they don't have letters, I am certain that many people who should be paying the charge will not do so, but that is another issue.

Anyway, my question is how does brought forward unused relief affect matters?  I worked through the HMRC example - Tracey - in PTM056410 and concluded that my client could ask the scheme to pay most of his charge but am now having doubts.  It is probably easiest to look at a real example (figures rounded):  Pension input amount £73K, taxable income £127K. Tapered annual allowance  £15K.  Brought forward unused pension relief £20K. The charge is due on £38K after deducting reduced annual allowance and brought forward relief.  £24K is payable at 45% (9.5K) and £14K at 40% (£6.5K), total payable £16K.  Still with me?  Tracey indicates that  'scheme pays' is on the excess of the pension input amount (£73K) over £40K which is £33K.  As the charge is calculated on £38K, the tax related to £33K of this can be paid by the scheme.

For this to be correct, it seems that b/f unused relief is effectively set against the pension input amount falling into the band of pension inputs between (in my client's case) £15K and £40K, rather than the element £40K upwards. Is this right?