0630, the patent for the original Starduster located at Patent US4208662 - Omnidirectional, vertically polarized antenna - Google Patents tells us the radial angle is 12*/25* degrees, and it is preferable at 17* degrees.
When I physically measured the radial angle for one of my SDr's it was 17* degrees. I took my dimensions from center of element to center of element to be more accurate with the lengths in the angle. The hub is off-set a bit from the center of the mast so the element tends to be electrically longer that its physical length and that will make a little difference.
When I take the dimensions for the Sirio I received from someone on the Internet, I found the radial angle was close to the 25* degrees. However, I did not physically measure the dimensions I used, and I might have only been give the physical length of a radial as noted in the specs and the length between the tip of a radial and the outside of the mast to calculate the angles. Since center to center may not have been considered, this 25* degrees may be off a bit...but it won't be much.
I used this calculator Right Triangle Angle And Side Calculator and I used 31.5" as noted in the specs for the top element for the radial and I used 12" for the plastic insulator that creates the angle.
The Sirio looks to be wider in the radial angle using the dimensions below noted in the antenna images. These are the dimensions I used in my Eznec model for the Sirio M400.
