The website recommends 1 per mil and if you did that. . . you'd have to put a sweater on to pass gas.
Here is what Perfumer's Apprentice recommends:
Koolada 10% PG
Koolada (menthyl methyl lactate) is used specifically to give that "cold" feeling at the back of the mouth.
It does not really have a 'taste', but it can be used in conjunction with menthol. Try using
4 drops per 4ml of eliquid.