We have tested "Robusta" and it works perfectly mounted onto any material with the exception of a circuit with currents under the antenna: it seems normal, I am wrong?
How we should place the antenna integrated into a circuit? How horizontally far from conductive nets? Better solid GND or copper cut-ut below the antenna?.
Our circuit is tiny in comparison with the antenna and also has other printed antennas so we are not sure if it ir viable or not using your antenna.