I have yet to fire up my 22 and I don't use any control beyond tweaking the bottom vents, but I've been smoking satisfactorily on my 18.5 and mini-WSM for several years now.
Tell us more about your process. What temperature are you going for and how are you measuring? Are you foiling the butts or just leaving them on the grate for the whole cook. What temperature are you pulling them at (though that shouldn't matter much - I think most smoke flavor is picked up during the earlier portion of the cook.
How do the butts look when they come out? A very dark color indicates smoke. A pink layer directly under the dark surface is also a good sign (the smoke ring.) Do you see these?
Also realize that a butt has a lot more interior than exterior. You won't get the same proportion of smoke as you get on something like ribs which have a lot more surface area.
If you have a Woodman's near you (I use the one in North Aurora) they have boneless rib tips that have more surface area and smoke up pretty good. I used them until they got more expensive than butts at Sam's.
Hickory and oak should be a good combo for pork. I also use apple and maple which you should be able to find locally (perhaps even in your own yard.)