INA219: Can I measure less than 1mA precisely with INA219? If so, how?

I am using an INA219 current/power monitor to measure the output of a small PV panel under low-light conditions over a period of several days. The short-circuit current (from a multimeter) is never above a mA for the size of panel I am looking to test. The INA I am using is on an Adafruit breakout board, and I am controlling it using an I2C interface to a Particle Electron. I have been using the Adafruit code library available on the Particle IDE for my purposes, which works well for larger panels with a bigger output, but there is no function that will allow me to change the settings to make the desired measurements.

My primary question is: Is it possible to make the measurements  required with reasonable precision (down to a uA if possible, but 5uA is acceptable) using the INA219?

If it is, I could do with some help with the implementation,

What I have done so far:

The library I have been using includes functions to change the input range of the INA, the options included are 32V/2A (default), 32V/1A, and 16V/400mA. I have tried adapting one of these functions to work for 100mV/1mA, the code for which I have included below. When testing it, I initially got better numbers (bigger, so implying that I had succeeded in changing the gain), but these no longer made any sense in context - as the output should be in mA, but the output readings were now much too big. I thought this was to do with the "ina219_currentdivider_mA" value which was then at 20, but changing it to a larger number returns to the original problem of the readings not registering such a small current (for some reason the output the library code gives is limited to two decimal places, I'm not sure why, if anyone could explain that as well I would be grateful). 

For background, I have a basic grasp of C++ language and a theoretical understanding of things like I2C and bit-wise communication, but am not very well equipped for low-level programming of these things, can anyone point me to a good resource about them that would help me be a little less dependent on libraries?

void Adafruit_INA219::setCalibration_100mV_1mA(void) 
{
  //declare variables
  float VBUS_MAX;
  float VSHUNT_MAX;
  float RSHUNT;
  float MaxPossible_I;
  float MaxExpected_I;
  float MinimumLSB;
  float MaximumLSB;
  float CurrentLSB;
  uint32_t Cal;
  float PowerLSB;
  float Max_Current;
  float Max_Current_Before_Overflow;
  float Max_ShuntVoltage;
  float Max_ShuntVoltage_Before_Overflow;
  float MaximumPower;

   VBUS_MAX = 0.05;              //in V
   VSHUNT_MAX = 0.1;           //(Assumes Gain 1, 40mV)
   RSHUNT = 18;                 //(Resistor value in ohms)
  
  // 1. Determine max possible current
  MaxPossible_I = VSHUNT_MAX / RSHUNT;      //0.005A = 5mA

  // 2. Determine max expected current
   MaxExpected_I = 0.001;         //1mA
  
  // 3. Calculate possible range of LSBs (Min = 15-bit, Max = 12-bit)
   MinimumLSB = MaxExpected_I/32767;   //3.05 x 10^-8 = 0.03uA 
   MaximumLSB = MaxExpected_I/4096;     //2.44 x 10^-7 = 0.24uA
  
  // 4. Choose an LSB between the min and max values
  //    (Preferrably a roundish number close to MinLSB)
   CurrentLSB = 0.00000004; //(0.04uA per bit)
  
  // 5. Compute the calibration register
  Cal = (String(0.04096 / (CurrentLSB * RSHUNT))).toFloat();                                     //This is a hotch-potched version of "trunc()" because the IDE was not compiling "trunc()"
  ina219_calValue = Cal;

   // 6. Calculate the power LSB
   PowerLSB = 20 * CurrentLSB;
  
  // 7. Compute the maximum current and shunt voltage values before overflow
  Max_Current = CurrentLSB * 32767;
 
   if(Max_Current > MaxPossible_I){ 
      Max_Current_Before_Overflow = MaxPossible_I;
   }
   else {
      Max_Current_Before_Overflow = Max_Current;
   }
  
   Max_ShuntVoltage = Max_Current_Before_Overflow * RSHUNT;
  
   if(Max_ShuntVoltage >= VSHUNT_MAX) {
      Max_ShuntVoltage_Before_Overflow = VSHUNT_MAX;
   }
   else{
      Max_ShuntVoltage_Before_Overflow = Max_ShuntVoltage;
   }
   
  
   Max_ShuntVoltage_Before_Overflow = VSHUNT_MAX;
  
  // 8. Compute the Maximum Power
   MaximumPower = Max_Current_Before_Overflow * VBUS_MAX;

  
  // Set multipliers to convert raw current/power values
  ina219_currentDivider_mA = 33333;                                          // Current LSB = 0.03uA per bit (1000/0.03 = )
  ina219_powerDivider_mW = 1;                                                  // Power LSB = 1mW per bit

  // Set Calibration register to 'Cal' calculated above 
  wireWriteRegister(INA219_REG_CALIBRATION, ina219_calValue);
  
  // Set Config register to take into account the settings above
  uint16_t config = INA219_CONFIG_BVOLTAGERANGE_16V |
                    INA219_CONFIG_GAIN_1_40MV |
                    INA219_CONFIG_BADCRES_12BIT |
                    INA219_CONFIG_SADCRES_12BIT_1S_532US |
                    INA219_CONFIG_MODE_SANDBVOLT_CONTINUOUS;
  wireWriteRegister(INA219_REG_CONFIG, config);
}

float Adafruit_INA219::getCurrent_mA() {
float valueDec = getCurrent_raw();
valueDec /= ina219_currentDivider_mA;
return valueDec;
}