You are probably neglecting to apply loc rot scale after import.
You should change the overall scale to be in cm so that it matches unreal.
You can try my plugin - when you import the rig the first time it sets the scale to what it needs to be.
http://mosthostla.com/gamedev/bonebreaker/
After the first import, delete everything from the scene and save your start file.
next time you import something the scale will remain set.
applying loc / rot / scale only matters of you scale rotate or move the armature.