There are a lot of reasons they make different heat range plugs. A lot of things need to be taken into consideration, chief among them, the compression ratio, second to that, I would think, is the rpm range. I don't know all the technical terms, but I'm pretty sure that the plug that works in a stock, low compression gasoline engine, would not be the ideal plug for a high compression alcohol burning engine.
Let's face it, there must be a reason spark plug companies make so many different heat range plugs. I'm not totally sure of all the reasons why, but I'll that one of them is the service each plug has to operate in. Low rpm and a lot of idling would call for one plug, high rpm and a constant load another. In my two cycle days, with the McCullough's, I ran one type and heat range of plug, and with the Rotary valve (much higher compression) I ran a much colder plug. The komet's even used a retracted gap plug. Very cold! With the McCullough's, when we ran alcohol, we ran a colder plug than when we ran gasoline.
Maybe the reason you're fouling these plugs (I think they were designed for low rpm's and light loads) is because they're so hot, you have to run a lot richer. You know, it surprises me what low CHT readings people get with alcohol. It may be that their plugs are too high a heat range and that it causes them to need a richer mixture, which holds down the heat. I don't think alcohol Burns cooler than gasoline, if it did, how could it make more horsepower?
I'm certainly no expert on four strokes, but if I was racing them, I would be investigating what the manufacturers of those spark plugs are saying.