#include <bits/stdc++.h>
using namespace std;
const int MOD = 1000000007;
int mod(int x, int m) {
  if (x < 0) x += m;
  return x % m;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    vector<int> v(n);
    int mx = -1;
    for (int i = 0; i < n; ++i) {
      cin >> v[i];
      mx = max(v[i], mx);
    }
    int ans = -1;
    for (int i = 0; i < n; ++i) {
      if (v[i] == mx) {
        if (i != 0 && v[i - 1] < v[i]) {
          ans = i;
          break;
        } else if (i != (n - 1) && v[i] > v[i + 1]) {
          ans = i;
          break;
        }
      }
    }
    cout << ans + (ans != -1) << '\n';
  }
  return 0;
}
