The compact pan/gain sliders control the first track from bottom up in the chain that has enabled gain or pan. By default track lanes have enabled the gain/pan controls, so that makes the sliders pre fx. You can disable the gain/pan on the lane track, and enable gain/pan on an fx track further up the chain to make the sliders post fx. A quick glance at the inspector group panel can tell you where in the signal chain the gain/pan controls are inserted.