Welcome to the forum, ihwf_vp:
Those signals are listed as Tropo, which means they will never be reliable because they depend upon atmospheric conditions that are favorable for tropospheric propagation.
https://www.google.com/?gws_rd=ssl#q...ic+propagation
http://www.dxinfocentre.com/tropo_eur.html
http://www.dxinfocentre.com/propagation/tr-modes.htm
I think you are doing very well. Enjoy them while they are coming in. They will continue during the summer, and then be less frequent later in the year.
Theory says that you can not receive signals that have a Noise Margin of less than -15 dB because that is the Thermal Noise Floor. Obviously, you are receiving them because they are coming in stronger than listed because of tropospheric ducting.
It is possible for you to hunt for an antenna with a little more gain, and maybe a preamp with a slightly lower noise figure, but I doubt that it will make much difference. You will still be at the mercy of atmospheric conditions.
Yes, distance is a factor, but so is the curvature of the earth which blocks the signals. If you click on the KTVI callsign in your report you will see the terrain profile. The black arc at the bottom of the profile is the curvature of the earth. The transmitter is on the left and your location ls on the right.
http://www.tvfool.com/?option=com_wr...ALLTV%26n%3d24
If you do experiment with other equipment, you need to know that you have a very strong FM transmitter only 2 miles away that might interfere with TV reception.
http://www.fmfool.com/modeling/tmp/9...b/Radar-FM.png