Welcome to the router forums.
The base made for the router is an equilateral triangle (all 3 sides the same dimension).
The size of the base is determined by the radius you want in the corners. The base is made using this radius as the distance from the center of the bit to one corner of the triangle.
The inside dimension of the frame/template that the base follows is determined buy the width and length of the cut you desire plus 2x the distance from the center of the bit to the center of one side of the triangle. The frame sides can also be curved so you can actually have a large radius, like at the top of the door panel, however any radius of the side of the frame/template has to curve away from the center of the panel.
Here is a link to a free triangle calculator.
If any input is 1 decimal the results will be one decimal so, I would input everything, angles and side dimensions, to 3 decimal places so you can round however you choose. Triangle Calculator
You want a 2.00" radius in the corners
In the top box of the calculator enter 30.000 (half of the angle of an equilateral triangle), in the right box enter 2.000 (the radius you want), in the bottom box on the right enter 60.000 (the complementary angle of the right triangle)
When you click the compute button it will show 1.732 for 1 side, 1.000 for the other side (this is your offset from the template), and 90.000 for the angle between the 2 sides.
Hope the picture helps. If you have any more questions I will attempt to answer them.