Thanks, Frank. IIRC, Kowa says to twist the eyecup fully inwards (like for glasses wearers). I was getting a clean circle but I suspect it's simply a limit of using a phone for digiscoping and that it will be better for casual photography. However, I wouldn't share that sparrow photo other than to show the issue I had.
I've been trying to avoid buying a long lens for my Nikon D7200 (although it may be worth trying the adapter for a DSLR before I get too far into things.)
Minolta 6x20, Vortex Fury 6.5x32, Jason 7x50, Nikon SE 8x32, Zeiss Conquest HD 8x32, Zeiss Terra ED 8x42, Zeiss Victory HT 8x42, Zeiss Victory 10x25, Canon 10x30 IS, Garrett 25x100 IF, Kowa TSN-883 w/25-60x WA, Televue Pronto, Televue TV-85