Awesome. That is pretty much exactly what I was thinking of doing. My thought was that you could more easily weatherize something like this rather than a parabolic dish which has a lot of wind loading.
Based on the literature the measure would be 6dBi (relative to isotropic). This is often referred to as 'gain' as it represents sensitivity to the band of interest at a given angle of arrival.
In the paper they were measuring signal gain between two antennas, and as such the 6dBm gain appears to be the effect of collating more of the beam spread into the receiver (as one would expect of a lens). Given my schedule I don't think I'll have enough time to print one by November but it would make for some excellent discussion! Reading the permittivity paper that was linked here was also quite good and I'm wondering if something could be integrated into openEMS which would tie the two together.
I'm also tickled by the idea of a 'Newtonian' RF telescope using two lenses.
What filament did you use?