In the pic I see a few issues as to being able to control the overall lighting levels as to ambient fill requirements and with an area of this nature you would want to start with a base as to as you say a uniform lighting level to be able to see the area with out hot and cold shadowed zones.
Of key interest is lighting elements, such as point lights, are photometric in nature as in they are based on real world lighting models as to falloff values and obtaining a uniform level of lighting is almost impossible to obtain a true renderosity effect on their own. For example you can see your already getting the red X which indicates you have to many lights overlapping.
What is interesting is in most game engines rendering techniques used in apps like Maya or 3ds Max, or even Blender, are transferable so we can steal a few ideas as to lighting and make use of them in Unreal 4.
Sooo
To start lets remove all of the lighting elements and begin by painting the canvas, so to speak, by first establishing our base ambient fill using a postprocess and a Ambient cube (HDR) map.
As you can see you can effect the fill with out increasing direct lighting levels
Another trick is if you have one area that needs more fill than another you can either overlap a postprocess and blend it in or make an ambient fill light by turning off inverse square shadows and cast shadows creating a fill only lighting element.