i dont know about others but for me my method of making FM is, lets say if i'm making 180ml FM, i will pour around 120-140ml of room temp water with 40-60ml hot water. usually will turn out to be warm, a 'just nice' temp for dear son.
Your Grandma is right, dont shake the milk. Use a spoon to stir instead. By shaking the bottle, there will be more 'air' trapped inside and baby will suck in the air..