Bypass humidifier- where do you measure delta T

I have a bypass humidifier on a forced air furnace in dry Denver. The bypass raises the return temperature 10-12 degrees. It looks like the last guy to look at this new furnace took the temperature of the return (for delta T) before the bypass? Shouldn’t it have been taken after the bypass? Doesn’t the furnace manufacturer specify the delta T based on the air where it enters the furnace? Not someplace else in the system. Thanks

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