#include <bits/stdc++.h>
using namespace std;
void solve(void) {
  int n, m = -1, in;
  vector<int> vet;
  cin >> n;
  vet.push_back(1e9 + 7);
  for (int i = 0; i < n; i++) {
    cin >> in;
    m = max(m, in);
    vet.push_back(in);
  }
  vet.push_back(1e9 + 7);
  for (int i = 1; i <= n; i++) {
    if (vet[i] == m && (vet[i - 1] < vet[i] || vet[i + 1] < vet[i])) {
      cout << i << endl;
      return;
    }
  }
  cout << -1 << endl;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  int t;
  cin >> t;
  while (t--) solve();
  return 0;
}
