Snap and KDE systray


I noticed that the programs that I packed in the snap format have a small icon in the KDE system tray.

A program without snap technology may have a normal icon, or it may be just awful, as in the example with DocFetcher.

I use interfaces
plugs: [network, network-bind, x11, home, unity7, desktop, desktop-legacy, gsetting, wayland, optical-drive, removable-media]

What to do when packing in a snap? What needs to be added to stage-packages? What is the preferred format for icons (PNG or SVG)?

Help advice.