OV9281 UVC FPS drop with trigger


I am trying to use my UC-762 (USB+OV9281 sensor) with Arduino UNO R3 board as the triggering source.
The documentation says that “In the case of MJPG 120fps, the external trigger frame rate can reach up to 100fps;” But the best frame rate I can get with trigger is 50 fps.
Auto exposure is disabled:

Arduino script is taken from from Arducam USB synchronization example, I tried different delay values (100/8, 10/20, etc.), but never managed to get over 50 FPS

byte led = 2;

void setup() {  
  pinMode(led, OUTPUT);

void loop() {
  digitalWrite(led, HIGH);
  digitalWrite(led, LOW);

Thank you for your help