There are no magic numbers, and they are quite resolution dependent sadly.
The stock default values don't do almost anything at all. For the effect to be visible, even on subconscious at higher than 3K resolution, it looks bad when doing IR tests at lower res..
I think it's not great solution.
I try to use at least 0,85 Pixel radius for sharpening, regardless if it's Corona, or Photoshop. This value can stay more of less regardless of resolution, unlike blur which needs to increase at higher resolution.
At low resolution the renderings are blurry because of the Filtering stock value being 2 pixels ("HQ Filter"), but even 1.5" Tent is quite blurrying..
Because I render my images at 4K to 8K resolution in most cases, my Blur value is 1.5+ I think.