#include <bits/stdc++.h>
using namespace std;
void solve() {
  int n;
  cin >> n;
  vector<int> a(n);
  int m = 0;
  for (int i = 0; i < n; ++i) {
    cin >> a[i];
    m = max(m, a[i]);
  }
  int res = -2;
  for (int i = 0; i < n; ++i) {
    if (a[i] == m) {
      if (i > 0 && a[i - 1] != m || i < n - 1 && a[i + 1] != m) {
        res = i;
        break;
      }
    }
  }
  cout << res + 1 << endl;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout << setprecision(32);
  int t;
  cin >> t;
  while (t--) solve();
  return 0;
}
