Mark - Some advise for Sudan... ZERO flash and ZERO UV in any of your materials.. even your eyes.. check all your flies under UV lights...
Peter Coetzee has just come back from a very successful trip with Tourette... he hammered the Triggers... but said any fly that had any Flouro/UV to it, even when not seen with the naked eye, but showed any UV glow under a UV lamp, was like throwing a rock in the water at the fish.. they bolted immediately!
So his Flexo's all had UV in them, and as such were useless... something worth thinking about when you tying another batch up, if they specifically for Sudan.. His Trigger Crack and Tan Merkins were the best flies...
Also key element of this fly is the weighting.. tough to see from your images where your Tungsten Dumbbells are, but the need to be positioned closer to the bend of the hook, rather than the middle of the body, to assure the fly sinks correctly and rides hooks up... learnt this from James Christmas the other night while tying with him...
I've also reverted to a different way of tying the eyes in which is more durable..
Instead of premade the eyes, I loop a piece of Mono through the Flexo from the "opposite" side, and poke the two ends out where you want the eyes to be... then slip on a glass bead in whatever color, and snip the mono then burn the mono with a Bouz Line Cutter or normal lighter... then you can coat with UV or varnish etc whatever.. Basically this means the eyes are on one continuous piece of mono, which is looped/threaded through the flexo, and as such don't pull out during fishing as easily..