FW Menthol is the menthol I use, at 5% standalone, and that puts it on the strong side (for me, not a huge menthol fan but I always keep some on hand as a palate cleanser). I don't have their Blue Ras, but I did combine the menthol with OSDIY Blue Ras. Slush and apparently it's good, since I have to mix a bottle a week for a friend who loves it. (Personally I don't care for it much, but again I'm not a menthol or blue raspberry fan) That mix is 2% FW Menthol, 8% OSDIY Blue ras. Any higher on the menthol and it starts amplifying the blue ras in unpleasantly chemical ways. Whatever % you decide on for your FW Blue ras, I'd try it at a 1 to 4 ratio first, then bump up the menthol if you see fit.