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I can't speak to FI tuning as I've never touched it.
But, to address your question about running as much DI as you can, Doug, for the most part, yes you should. As Andrew mentioned, there's the charge cooling aspect to DI. But charge cooling isn't just dependent upon how much fuel is being injected via direct injection but also when the fuel is injected. When tuning a specific condition and a fixed amount of fuel, maybe you change the pfi/di ratio from stock to allow more fuel on the port side to allow for good mixing and then slightly retard the DI timing so the fuel mass from the DI side cools the cylinder (air inside gets denser -> more air can come in -> higher volumetric efficiency -> more power).
Andrew and Mike also touched on how charge cooling allows for operation at high compression ratio. By cooling the charge air and cylinder, you're directly affecting where the onset of knock will be in relationship to spark timing (cooler cylinder temps mean lower chance of fuel igniting on its own).
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