Join Date: Oct 2007
Location: corvallis, Oregon
That's a challenge to get just right. The profile shape on the top edge of the lower cabinet makes it an issue. i have a couple possibilities for you, neither of them perfect.
1) you can set your horizontal filler piece right at the bottom edge of the profile, so probably about 1/2" or so beneath the level of the top. You can also set the front vertical filler back the same distance from the cabinet face so that your whole filler is recessed from the faces of the cabinets. It will at least be an intentional and uniform look.
2) If you really want everything flush and the fillers not readily obvious, well, you could rout out a small rabbet into the edge of the cabinet top where the profile is, eliminating that profile. Glue in a new strip of wood along that edge, sand it flush, and paint it to match the cabinet. Essentially, get rid of the roundover profile on that side edge.
I cannot, just now, think of another way to render the fillers unnoticeable. Someone may suggest making the edge of your filler strip to fit flush against the profile. For instance, if the profile is a 3/8" round over, you can make your filler strip with a 3/8" cove to fit right over the round over. You can try that, but I see two issues with it. First, the top edge of the cove would be so thin that it would be susceptible to chipping off. If you glue it tightly to the round over, you may eliminate that problem, but you would likely need to first sand the paint off of the round over in order to get the glue to adhere well.
That's the best I've got for you.