I've needed 30+ drops in a new dry fan driven unit. Usually 20 will due after that. 10 drops if I'm topping off a still smoking unit on the tracks after a few minutes of cool down. I've never got anywhere with 5 drops.
I'm a big MTH PS3 guy for smoke like Arnold but I have to say my 5 or so lionel engines from more recent years smoke just as well.
From what I've heard lionel has come a long way with their smoke in recent years. Not to mention JT Mega steam was a game changer in my opinion.
Brad