#include <bits/stdc++.h>
using namespace std;
void solve() {
  long long int n;
  cin >> n;
  vector<long long int> a(n);
  ;
  for (long long i = 0; i < n; ++i) cin >> a[i];
  long long int mx = INT_MIN;
  long long int flag = 0;
  long long int pos = 0;
  ;
  for (long long i = 0; i < n; ++i) {
    if (mx < a[i] && (a[i] > a[i + 1] || a[i] > a[i - 1])) {
      flag = 1;
      mx = a[i];
      pos = i;
    }
  }
  if (flag == 0) {
    cout << "-1";
    return;
  }
  cout << pos + 1;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  int test;
  cin >> test;
  int x = test;
  while (test--) {
    solve();
    cout << "\n";
  }
}
