To me, it looks like the easiest and most reliable way to tune fuel (without messing up any other load tables) would be to use the Engine Load Compensation (MP) table. Looking at the map though, there is not much resolution for boost. I only have two columns. Will it work if I reduce the number of vac columns and add more boost columns?
You're going to affect other load-based tables regardless of which table you use to make your fueling adjustments. Suppose your ECU thinks it's pulling 2 g/rev at 4000 RPM in the middle of a pull... if you add 10% to the corresponding cell in the MAF scaling, it's going to think that it's pulling 2.2 g/rev under the same circumstances. Or if instead you add 10% to the corresponding cell in the Load Compensation table, it's still going to think that it's pulling 2.2 g/rev under the same circumstances. Either way it will start using the fueling and timing from cells slightly to the right of the ones it was using before, even though the actual load is exactly the same.
Your corrections may not actually be 10% but you get the idea.
To reduce AFR errors that consistently correspond to a particular MAF voltage (regardless of RPM or load), adjust the MAF scaling. To reduce AFR errors that correspond to a particular load and RPM (regardless of MAF voltage), adjust the Load Compensation table.
And yes, you can revise the row and column values if you want. My columns run from -10 to +22, and they're not evenly spaced but they give me resolution where I needed it.