Where to add Mash Ph adjustment acids

Just wanting to clarify something that's been bugging me with the Beersmith Ph calc.

I'm brewing an IPA next weekend. It's a 19-litre batch and I'm preparing 33.35 litres in the liquor tank to cover mash, sparge and to account for boil off and volume left in the kettle. I will add 7.9 litres for the mash, another 7.9 litres to bring the temp up for the mash out and then 17.55 litres for the sparge.

The "Final Mash Ph Adjustment Tool" has indicated I should add 4.2ml 85% phosphoric acid to "use in the mash". This may sound like a dumb question but this means I add 4.2ml to the 7.9 litres for the saccharification rest right?

I just want to make sure I shouldn't be adding this adjustment to the full 33.35 litres in the HLT.

Thanks,

You want the mash pH during the saccharification rest to be in the target temperature range.  If you make a pH adjustment, you want to make it at this step.