I am familiar with the "Improved Sparkle Dun", but not the "Modified Sparkle Dun".
I was reading the wonderful book "Mayflies" by Knoff and Cormier. In it, they discuss the 4 stages of the Emerging Mayflies. They mention, in passing, using a "Modified Sparkle Dun" which they said they would elaborate on later in the chapter. They only referred to the "folded back position" of the wings. I never found any other info on it later in the chapter. Perhaps I missed it.

Anyone familiar with this version of the Sparkle Dun?

I thought, based on the reference above, it might just be like this instead of vertical winging fibers?

Thanks for any info you can provide for documentation and the source of the info.