The 1/4 tank isn't critical.
They just want you to use a decent amount of fuel to help get it more accurate.
Keep an eye on what it says over the next few tanks after the 2nd fill as well and if it is consistently low or high you can tweak it a tad more.
I used to fill my truck from an empty sub and 1/4ish main (long range) so it would take 110 to 125 odd litres.
There are variables from pump to pump but it should be within about a litre or maybe two at the most and over several fills it should average out.

My Scangauge fuel % setting for my Patrol was +9.7%
That was with a DP Chip set on 7 or maybe 8 can't quite remember.

I can't remember what the speed compensation % was but that is easy to set.
Just set it to agree with a GPS or SatNav it will be different for almost any truck due to tyre diameter and wear.

You need to have both fuel and speed corrections set correctly to get the best accuracy