Making an accurately centered cove on end grain with sandpaper was hit or miss for me. After cutting and dry fitting the acute angle on the plank end, I clalmped the strip in a wood faced vice, cut surface up. Using a Japan pull saw I cut a 1/16th deep groove in the center of the cut surface. Using a triangle file, I opened the cut to a V-shaped groove. Using the small end of a rat-tail file I opened the groove to a cove. Sandpaper folded over a bead scrap then smoothed the cove for a tight fit. The whole thing takes less than a minute.
Cool. That's the tale of a man with sharp hand tools. Got any pictures?
Laszlo