For the starting you should always try tweaking the Lightmass properties in world settings, if results are unsatisfactory then we will tweak the baselightmass.ini, that too with caution, increasing individual values and noticing there effect. It’s a good point to start from tweaking values in [DevOptions.StaticLightingProductionQuality] and then moving to the other options like [DevOptions.PhotonMapping]. Always try to move in incremental steps. For better understanding of baselightmass.ini you can try downloading “sceneExport.h” file from source code of unreal engine on git-hub it contains explanations of the parameters given in baselightmass.ini.