To improve the size of your runway lights add these line under fs9.cfg / Display:

RUNWAY_LIGHTS_SURFACE_SCALAR=1.0 //scales edge, center,end,touchdown,runways
RUNWAY_LIGHTS_VASI_SCALAR=1.0 // scales VASI lights
RUNWAY_LIGHTS_APPROACH_SCALAR=1.0 // scales approach light bars
RUNWAY_LIGHTS_STROBE_SCALAR=1.0 //scales RAILs and ODALs

The smaller the value, the smaller the light size. These are floating point values, in other words you can use 0.5, 0.005, etc.