DCS EFM/PFM Ground Effect Bug

//Ground Effect Bug described in code
//Fix shown below and is working perfectly well in three EFM aircraft I've developed

void ed_fm_set_surface(double       h,//surface height under the center of aircraft
    double      h_obj,//surface height with objects
    unsigned    surface_type,
    double      normal_x,//components of normal vector to surface
    double      normal_y,//components of normal vector to surface
    double      normal_z//components of normal vector to surface
    )
{
    double altitudeAboveTerrain = alt - h;  //alt is from ed_fm_set_atmosphere
    double altitudeClearance = alt - h_obj; //this clearance becomes negative when underneath another aircraft, bridge, aircraft shelter, etc.

    double groundEffectAltitude = altitudeClearance;

    //why negative altitude matters:
    //equation for ground effect influence on lift:
    //CLge_mult - ground effect lift coefficient multiplier
    //b - aircraft wingspan (m)
    double CLge_mult = CLge_mult_table->getValue(groundEffectAltitude / b); //table lookup to get multiplier

    //Here is a lift coefficient multiplier table that is typical
    // h/b is the independent variable and is always supposed to be positive, as you should never fly underground
    //          h/b         CL mult
    //  *CLge_multTable
    //       0.054000  1.250000
    //       0.100000  1.160000
    //       0.200000  1.096100
    //       0.300000  1.060000
    //       0.400000  1.040000
    //       0.500000  1.030000
    //       0.600000  1.024200
    //       0.700000  1.021300
    //       0.800000  1.016100
    //       0.900000  1.010000
    //       1.000000  1.000000;

    //This means 25% increase in lift when a negative groundEffectAltitude is used.

    //How to fix:
    if (altitudeClearance < 0)
        groundEffectAltitude = altitudeAboveTerrain; //use this altitude whenever the other method gives a negative.
}