I guess you are having trouble distilling it down, so let me.
Cruz is against a program that costs tax dollars, redistributes wealth, and harms every American driver.
Trump is for that program, supports the continued existence of the administrating agency, and supports the continued harm it does to every driver and taxpayer--an obvious pandering to the Iowa Ethanol Lobby (including the Governor), OR, just selling America down the river for the status quo.
I don't consider anything about the latter "Conservative".
Cruz's stance against the ethanol mandate and subsidies is a stance against redistribution of wealth and a one-size-fits-all policy that costs Americans a tenth of their fuel mileage for an 'emissions problem' that might not even be a problem where they live, regardless of where they live--and he's taking heavy flak for it, in a state where the Ethanol Mandate is seen as big bucks for the state.
Does that clarify the issue any?