Use ServiceName instead of ServiceReferance. It's very Easy
Here is an example for SVT 1 HD:
If the IPTV Channel name is SW SVT 1 HD VIP for example
The picon name will be swsvt1hdvip.png
Or even easier. Use Dreambox Edit and import your Favorites/Bouquets from your decoder.
Now open the IPTV list where you want to add picons.
The list is in the right window/box And the satellite list is in the left box.
Now find in the satellite window the matching channel, hold the CTRL button on your computer keyboard pressed
Now drag and drop the correct satellite channel on to the IPTV channel in your right window.
This does not only copy your picon referance, But also copy the EPG referance. So you now have both picons and EPG fixed
It works just the same with E-Channelizer if you prefer that instead of DreamboxEdit