Could be coals - QL's cook differntly than naturals.
Could be brand of tobacco - drier brands like more heat, not enough and you get no smoke.
Could be your brand of foil is thinner, thus why you need 2 layer (or rather are using).
Could be anything - normally, the less heat the less smoke = less harsher. Adding more heat allows the shisha to cook correctly and produces the normal amount of smoke - too much heat produces harsh/hot smoke and can burn.
But, as long as your getting it to work, it works. Trying to explain it could jinx is