Wenge is terrible for filling gain using just lacquer sanding sealer because it shrinks so much. Brandon Stahl used to use a polyester material for filling those grand canyon type slots, but i've never used it myself, or really know what to recommend for that stuff, but it might be worth researching it. What i do with that stuff is avoid using it as much as possible, but when i'm stuck with it i start with lacquer, then do a several wet coats using the auto clear coating. then i let it set a day, touch sand and do another wet coat. something about letting it cure for a day before sanding and recoating gives me a better build up....
It's the nature of the beast Bryan. That stuff is just a bear cat to fill.. It just takes more material, and you want to use a high gloss material with good solids for grain filling to ensure it doesn't shrink.that's why you wait a day for it to cure ... I'd look into the polyester material for a sanding sealer if you plan on using more of this Wenge....
btw ...Paduke is the same class, as well as Red Oak. Of course not many bowyers use red oak for risers.