3dB loss is half your power, not ideal, but I still got spots in Australia on 20M. I was not sure, at first, if my U3S, BPF or relay board was causing the low power. I came on this discussion group to pool knowledge. It turns out it was my BPF, so now I can move on and build and fit the 5 Watt amp knowing it will be driven correctly. I have now built a simple Watt meter 0 to 1 Watt, two 100 ohm resistors, a diode, a .1uF cap a 200K pot and 50uA small panel meter. Works fine. It matches my company's £5000 power meter within 5%!!
I am interested in seeing how my Cobweb performs on the higher bands 15-10M as I am not always on the air when the bands open.