"I find the Collings fret wire too wide. Especially as I go up the neck, I start to run out of room to put my fingers in."

Hear! Hear!

I find it much easier to play on a mandolin with traditional, "mandolin-sized" fret wire, for the exact same reason. Just as an important part of music is "timing", or "the space between the notes", [for me] a mandolin requires "space between the frets"!