Assuming it was the ALPHASIM T-6 I had a more closer look at the effect. The texture which is triggered by the effect is the FSX standard 'fx_smoke.bmp' texture. I have looked at the alphas and they are narrow, however the alphas in the texture are spread overe the complete texture.
What you say completely does make sense (for once :d ), as it is a general texture it will show like this in all effects which use this texture. Give me 5 minutes and I will zip the texture and attached it to this post.
Just unzip the texture and and put in in the FSX/effect/texture folder.
Cheers,Huub