Yes, you are in the ballpark. (from best I can gather.. as I am also wandering somewhat aimlessly through the same, said, ballpark)
So a few notes.. forgive the rambling.. but this is just a lot of what I learned recently about my own ecm and how FFV and alcohol content effects it.
I have a 2016 FFV Supercharged so we have basically the same ecm/truck. Mine is self tuned with HPT, however.
The 30% thing... yes, there are 2 "options" for most tables on the FFV. "30" and "75". That's in relation to ethanol. So less than 30 uses one and more than 75 uses the other.
NOW... thats NOT to say that there are not situations where the ECM may calculate based on BOTH those, say if you are at 25%... (ecm could say meet in between the 2... 60% "30" table/40% "75" table).
There may be black/white areas where it ONLY uses one or the other... but with such a complicated ecm I cant imagine they dont interpolate when in between.
As far as fueling. I had noticed I was getting much better fuel top end when the ecm thought there was high ethanol. So yes, it's definitely opening injectors longer.. however there are tables that we cant see that are also effected when eth is high.
So... what that means is we need to get ya close to "0".
I had significant problems with my tune being fueled well and then suddenly a day later being more lean. Every time I flashed it, nice and rich.. until a day later.
The ONE thing that was consistent is I was always showing high eth content. At first it was totally by accident.. I didnt realize it was so high. Later I raised it intentionally to see if it helped top end. (I was maxed on maf and PE tables)
Long story short, it DID add fueling but it was not worth the unpredictability of the tune in high eth mode.
So.. where this can help you... I can help move the eth content.
Do you have the ability to scan and modify the tune now yourself?
If you can post your tune and a scan here, or message me it, I should be able to get your content back to 0%.