Fill flash settings for the E M5 II?

I am still learning how to use my new E M5 II and have gotten stuck on the settings to use for fill flash with the included flash FL-LM3.

When I say fill flash, my meaning is that the overall exposure has already been set under the aperture or shutter priority modes. The flash is being used not to illuminate the scene but to either fill in the shadows in a backlighting situation or perhaps to add a 1/3 stop "pop" of light in a portrait situation.

I prefer to work in aperture mode. No matter what combination of settings I try I cannot achieve the fill flash i am looking for. I have experimented with the Custom Menu F third line setting in both the On and Off settings, have tried both Auto Flash and Fill Flash settings, and both 1st and 2nd curtain settings.The only method I have come up with is to set both the exposure and the flash compensation modes to manual. I could get used to manual exposure but in flash manual mode the flash comensation is measured in fractions of the power and not in f stops. For me this is totally unintuitive and not practical for fast moving street photograpjy.

Have I missed something or do I need to purchase a different flash that has its own compensation buttons on the flash. Help would be appreciated.

Thanks.