#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long t;
  cin >> t;
  while (t--) {
    long long n;
    cin >> n;
    long long a[n];
    long long maxi = INT_MIN;
    for (int i = 0; i < n; i++) {
      cin >> a[i];
      maxi = max(maxi, a[i]);
    }
    long long count = -1;
    for (int i = 0; i < n; i++) {
      if (a[i] == maxi) {
        if (i != 0 && a[i - 1] < maxi) {
          count = i;
          break;
        } else if (i != n - 1 && a[i + 1] < maxi) {
          count = i;
          break;
        }
      }
    }
    if (count == -1) {
      cout << count << endl;
    } else {
      cout << count + 1 << endl;
    }
  }
  return 0;
}
