The 19 foot length is just a starting point, if you follow the directions you will lengthen or shorten the overall length when you tune the antenna using standard SWR tuning methods. The overall length of the antenna is dependent on several things, not the least of which is the matching network. In this case as said matching network is not adjustable in and of itself it determines the overall length of the antenna for any given frequency.
When it comes to the radials, this isn't a resonant antenna such as a quarter wavelength antenna, so resonant lengths on the radials don't matter quite as much. As long as they are close, the antennas matching network will tune the overall antenna as a whole, and this includes the radials. That being said, they are already close if not a resonant length.
I'm curious, do they still advertise these as "not for 11 meter use"?
The DB