1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

#include <bits/stdc++.h>
using namespace std;
int called = 0;
void solve() {
  called++;
  int n;
  cin >> n;
  vector<int> vec(n);
  map<int, int> m;
  for (int i = 0; i < n; i++) {
    cin >> vec[i];
    m[vec[i]]++;
    if (m[vec[i]] == n) {
      cout << -1 << "\n";
      return;
    }
  }
  for (int i = 0; i < n; i++) {
    if (i == 0) {
      if (vec[i] > vec[i + 1]) {
        cout << (i + 1) << "\n";
        return;
      }
    }
    if (i == (n - 1)) {
      if (vec[i] > vec[i - 1]) {
        cout << (i + 1) << "\n";
        return;
      }
    } else {
      if (vec[i] >= vec[i - 1] && vec[i] > vec[i + 1]) {
        cout << (i + 1) << "\n";
        if (called == 8) {
          for (auto i : vec) {
            cout << i << " ";
          }
        }
        cout << "\n";
        return;
      }
      if (vec[i] > vec[i - 1] && vec[i] >= vec[i + 1]) {
        cout << (i + 1) << "\n";
        if (called == 8) {
          for (auto i : vec) {
            cout << i << " ";
          }
        }
        cout << "\n";
        return;
      }
    }
  }
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  int t;
  cin >> t;
  while (t--) {
    solve();
  }
}
