Sometimes we can't see the tree's because we are on the beach. Take a 1/4" rounding bit, assume it is a full 90°, because it should be, measure the OD, mine is 1.002", there are 2, 1/4" flutes on the OD line so they add up to 1/2", if you subtract from the 1.002"D, the .5" of the flutes, the center diameter should be .502" and measurment proves to that result.
Measurement of the height of the flute was .250". So if you set the bottom and the side of the cutter as KVOM stated, then move down and in .250" you wil be there for the full radius.
I find the a less than full radius appeals to my eye, so I would move it .200 down and .200 in. If it was a large but thin plate then .250 in and .150 down would look better.
I came upon this at one of lifes 'DUH' moments, so after missing up a piece with the wrong eyeball setting, I measured the bits and then said 'DUH' of course.