I've found focus peaking to be a dream with my K-30, even at longer focal lengths. I'm not sure how it can be 'too wide' - I find myself actually turning bright/dark highlighting on (effectively widening the shimmer) to cheat my way sometimes with it (with highlighting on, the focus 'shimmer' is interpreted as a highlight by the camera and glows yellow) due to it being too hard to make out.
I've used it with my clunky old budget zooms to great effect, so if a costly birding-capable lens is failing with it I'm not sure what to say except something sounds off with either the camera or your technique with using it.
To get an idea, when I picked up my M50 f/1.4, the first thing I did was go around shooting at f/1.4 because thats what I bought the thing *for*.
Focus here was on his left eye, ambient light was 'pretty darn dark apartment'.
Again, very poor light with me deliberately underexposing as well, focus peaking was on the foil.
The abovementioned old clunky zoom - a Sears 70-210mm. Any failings here were with that and not the camera. Focus peaking was on the edge of the light pole (not the birds). I dropped the aperture down to f/8 simply because I was hanging myself out the bedroom window with the camera cocked at a hideous angle as I used the abovementioned 'highlights on' trick in order to try to catch them. This would have been shot at 210mm. Using the OVF would have meant me having to learn how to levitate, which obviously wasn't happening.