I think it is more a ratio and dilution issue more than a mixing problem...
last winter I did a load of trials with mixes varying from 1% to 20% in temps from -1 to -12 which we had here in Holland and to be honest it all followed the physics...so you can see why I am very sceptical of these half coke can type claims

I also tried these tests with Methanol...pretty much the same...
bBut if you are really convinced about iso and like alcohols...you should really think about buying it in 200litre vats...much, much cheaper..I buy around 400litres a time...I also use it for making biodiesel so bulk is best..
Cheers
Dave