Adjusted net income vs. pension contributions

I have a NEST workplace pension, which is a "relief at source" type of pension. That means when I pay in X, Nest adds X*1.25 to my account. I also contribute from my net income to a private SIPP, and here too the pension provider takes X and automatically claims the basic 20% tax relief on it so that a few weeks after the initial contribution of X my account ends up with X*1.25. My question is: when calculating my adjusted net income - do I reduce my gloss salary by X, or by X*1.25? https://www.gov.uk/guidance/adjusted-net-income stars by saying "Adjusted net income is total taxable income before any Personal Allowances and less certain tax reliefs, e.g. pension contributions where your pension provider has already given you tax relief at the basic rate — take off the ‘grossed-up’ amount". The phrase is confusing for someone with EASL because it talks about taking things off twice, but I think this is saying that I should be reducing my gross income by X*1.25. But later it says "Take off any tax reliefs that apply like: payments made gross to pension schemes — those that have been made without tax relief". I do not know of a SIPP that doesn't automatically top up any contributions of X with the 20% tax relief. When this talks about "without tax relief" does it refer to salary sacrifice types of pensions, where the contribution is made before NI and income tax and therefore the pension provider doesn't top anything up with tax relief? I don't have one of those so don't know how they work. A little later the page makes it very clear that it should be X*1.25: "f you made a contribution to a pension scheme where your pension provider has already given you tax relief at basic rate, take off the ‘grossed-up’ amount — what you paid plus the basic rate of tax." But when I called 0300 123 4097 and was eventually put through to a tax free childcare eligibility advisor, they said that adjusted net income should be calculated by taking gross income and removing X worth of pension contributions, not X*1.25?!?! Finally straw -> I am a higher income tax rate payer, so shouldn't I be reducing my gross income by more than X*1.25? I find it all gross-ly confusing.

Hi,
This forum is for general queries only and is intended to help you self-serve. We are unable to provide specific advice tailored to individual circumstances. 
You may wish to contact our Income Tax team: 
Income Tax: general enquiries 
Alternatively, you may want to consider seeking professional advice. 
Thank You

Respectfully, I don't agree this is about individual circumstances. I am merely trying to better understand your own documentation, because it's unclear. Everyone in the UK has a pension, most are on the same "relief at source" type as me, and many also contribute to SIPPs out of their post tax income. Ceteris paribus, can you please better explain how adjusted net income is supposed to be calculated given contributions to those two pension account types?

Hi,
Details on adjusted net income can be found at Personal Allowances: adjusted net income
Thank you.