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;
const long long mod = 1e9 + 7;
void solve() {
  int n;
  cin >> n;
  vector<int> v(n);
  int maxi = INT32_MIN;
  for (int i = 0; i < n; i++) {
    cin >> v[i];
    maxi = max(maxi, v[i]);
  }
  vector<int> temp;
  for (int i = 0; i < n; i++)
    if (v[i] == maxi) temp.push_back(i);
  int index = -1;
  for (int i = 0; i < temp.size(); i++) {
    if (temp[i] == 0) {
      if (maxi > v[temp[i] + 1]) {
        index = temp[i] + 1;
        break;
      } else
        continue;
    }
    if (temp[i] == n - 1) {
      if (maxi > v[temp[i] - 1]) {
        index = temp[i] + 1;
        break;
      } else
        continue;
    } else {
      if (maxi > v[temp[i] + 1] || maxi > v[temp[i] - 1]) {
        index = temp[i] + 1;
        break;
      } else
        continue;
    }
  }
  cout << index << endl;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int tt;
  cin >> tt;
  while (tt--) solve();
  return 0;
}
