#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    vector<int> arr(n);
    int max = 0;
    for (int i = 0; i != n; i++) {
      cin >> arr[i];
      if (arr[i] > max) {
        max = arr[i];
      }
    }
    int ind = -1;
    for (int i = 0; i != n; i++) {
      if (arr[i] == max) {
        if (i > 0 && arr[i - 1] < max) {
          ind = i + 1;
        }
        if (i < n - 1 && arr[i + 1] < max) {
          ind = i + 1;
        }
      }
    }
    cout << ind << '\n';
  }
  return 0;
}
