Lopy 4 433 output power

[zeroro]

Hello,
What is the real maximum output power that can be achieve with the Lopy 4.
The datasheet seems to say +17 dBm or +20 dBm in boost mode, but we measure a maximum -14 dBm on several boards with no change when boost is activated.

[frecfrec]

Here is a minimal example that show the problem.
Expansion board V3.1 + Lopy4
Platform IO / C++

#include <SPI.h>
#include <LoRa.h>

int counter = 0;

#define LORA_SCK          5    // GPIO5  -- SX1278's SCK
#define LORA_MISO         19   // GPIO19 -- SX1278's MISO
#define LORA_MOSI         27   // GPIO27 -- SX1278's MOSI
#define LORA_SS           18   // GPIO18 -- SX1278's CS
#define LORA_RST          23   // GPIO14 -- SX1278's RESET
#define LORA_DI0          26   // GPIO26 -- SX1278's IRQ(Interrupt Request)
//#define LORA_DI0          33   // GPIO26 -- SX1278's IRQ(Interrupt Request)
#define LORA_FREQ_BAND    433E6

void setup() {
  Serial.begin(115200);
  while (!Serial);

  Serial.println("Init LoRa Sender");
  SPI.begin(LORA_SCK, LORA_MISO, LORA_MOSI, LORA_SS);
  LoRa.setPins(LORA_SS, LORA_RST, LORA_DI0);

  if (!LoRa.begin(LORA_FREQ_BAND)) {
    Serial.println("Starting LoRa failed!");
    while (1);
  }

  // set spread factor
  LoRa.setSpreadingFactor(8);  // defaults to 7, supported values are between 6 and 12
  LoRa.setTxPower(17); // TX power in dB, defaults to 17 - value from 2 to 20
  LoRa.setSignalBandwidth(125E3); // defaults to 125E3. Supported values are 7.8E3, 10.4E3, 15.6E3, 20.8E3, 31.25E3, 41.7E3, 62.5E3, 125E3, and 250E3
  // LoRa.setCodingRate4(codingRateDenominator); // defaults to 5, Supported values are between 5 and 8, these correspond to coding rates of 4/5 and 4/8. The coding rate numerator is fixed at 4.
  // LoRa.enableCrc(); // LoRa.disableCrc(); // by default a CRC is not used.
}

void loop() {
  Serial.print("Sending packet: ");
  Serial.println(counter);

  Serial.println("start to send packet ... ");
  // send packet
  LoRa.beginPacket();
  LoRa.print(millis());
  LoRa.print(" ");
  LoRa.print(counter);
  LoRa.print(" abcdefghijklmnopqrstuvwxyz");
  LoRa.endPacket();

  delay(1000);
  Serial.print("packet sent... ");
  counter++;

}