PEA (main ingredient in SI-1) is known to be a great cleaner but it plateaus in effectiveness at a certain point of concentration where more PEA doesn't equate more cleaning. I don't exactly know where that is.
I've personally used a full bottle of SI-1 to a full tank of gas in the Corolla several times. However my favorite use of SI-1 is to simply add 1 oz (yes, 1 oz!) to a full tank of gas every fill-up. You can actually feel it idling slightly better with that low concentration. I'm not sure it's super effective at cleaning in those small amounts, but it speaks to the power of it that you can notice a 1 oz concentration in a full tank of gas.
I think ChrisFix will get to SI-1 in his youtube fuel cleaning series soon - will be interesting to see. Based on other PEA-based cleaners he's tested it seems like most of them don't really clean the combustion chamber that well. He unfortunately doesn't test the injector cleaning effectiveness of any of them.