The way I understand injector slopes is this. The injector low slope is a value that can correct for the actual opening/returning delay of the pintle/disc (mechanical delay) that is inherent to a fuel injector. People often assume (not saying you) that just because they buy a batch of 8 injectors that have the same flow rating, that they will flow the same. Well they will usually not flow the same. There a lot of manufacturing tolerances that prevent that. There is a quirk with pintle and disc injectors. They behave very much like the valves in our valvetrain. They are subject to what is called "bump" just like our valves in our motor are subject to bounce when they close. The noticeable difference being that injectors are subject to a measurable bounce not only when they close, but also when they open. This can also increase the overall time that the injector is releasing fuel as compared to the actual commaned pulsewidth. I always recommend to people to buy flow matched injector if they want to get serious. The high slope is usually the actual flow rate of the injector.
The low slope is used absolutely when the perceived pulse width is less than the injector breakpoint. When the perceived injector pulse width equals or exceeds the injector breakpoint, then the high slope is used as an offset to the low slope. The offset is calculated by taking the difference between the high and low slope breakpoints, and then subtracting the result from the high slope. Like I mentioned earlier, the WOT Fuel Multiplier vs RPM is merely but one of the fueling parameters that we tune with. We do not exclusively focus on that particular table. I think that may be where the misunderstanding was. I think Matt was just, like I said, citing an example of one of the tables that need attention. I know he knows how important the MAF transfer function is.
The problem with relying on messing with the slopes to adjust LTFT’s, especially knowing how the low slope works, is that you can adversely affect the injector timing and/or offset vs. voltage. There are dozens of ways to go about dialing in the a/f, but I would much rather use things like ACT and load scaling, airflow references and MAF transfer to dial in the tune.