@bpleat,

I believe that you should have been able to do exactly what you are looking for through the smart actions feature of the app. The smart actions are not supposed to be limited to the device you are interacting with. If there is something that isn't working correctly with your smart actions, you may want to use a combination of the grouping feature and the smart actions feature. You could also trigger the scene that you have set up from the smart actions when the device turns on from the smart action configuration.

Many companies of began to phase out their support for IFTTT triggers as the cost placed on the companies to have triggers for their smart devices has grown to such an extent that it is no longer profitable to pay for the IFTTT integration. Your best bet for using a third-party service for controlling Kasa devices and creating automations would be the SmartThings app, as they are an official partner of TP-Link.