Thanks everyone for your comments.
I have fired an email off to Funke but after further testing, it does seem that the Funke only sends the info when it is being interrogated. I had another play today and whilst on the apron, I was getting nothing on the PAW even though the indicator on the Funke was flashing on odd occasions to say it was sending. Whilst moving the aircraft, I noticed that it would appear on the PAW traffic screen briefly and then disappear.
Then I flew the aircraft and took my laptop and 2nd PAW unit with me. During the flight, the Funke was appearing on the traffic screen as full ADS-B even with the correct value for SIL and SDA (set to zero as the LAA require).
When I landed and stopped, the Funke disappeared from the traffic screen and again whilst taxying, it would appear briefly and then disappear.
This is definitely not how I anticipated it would work. With the Trigs, as soon as your turn them to alt, they appear on the PAW traffic page all the time whether flying or not and whether being interrogated or not. Surely this is a mistake by Funke, I have now found another couple of people who say their TRT800H work the same way. According to any documentation I have read, a transponder with ES should broadcast at a regular intervals regardless of being interrogated by ATC.