I have this problem in three different versions of plasma on two different distros (I think KDE Neon LTS is built on Kubuntu 16.04, not positive though)

• Kubuntu 16.04 with plasma 5.5.5
• fully up to date Arch with plasma 5.9.4
• KDE Neon LTS with plasma 5.8.6

The screenshot is from Kubuntu 16.04 with 5.5.5. Is there any way to make the icons in kimpanel the same size as those in the system tray? I was previously using Kubuntu 14.04 with, I think, version 4.11.8, in that case kimpanel looked like it was part of the system tray. Thanks!