Special Effects Details in FSX

I currently have technical query over at Orbx regarding the detrimental performance at one of their scenery airports when I have my Special Effects Detail set to my normal setting of Mid to Full. I started getting 9fps and stuttering versus normal 30fps smooth. When i reduced the Special Effects to far left "low" I was back to 30fps smooth again.My question is: can anyone of you who know the in's and outs of FSX tell me what this slider actually effects. I know it effects wave motion & fireworks but is that it ? I notice that on Low setting I still see smoke from cooling towers etc. Also are these files in the regular FSX "Effects" folder. My confusion is to what effects are governed by "Effects" versus those "effects" that appear when the Scenery Complexity slider is set to norm/max.Would be grateful for any feed back.