#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  cin >> t;
  while (t--) {
    int n, mx = -1;
    cin >> n;
    vector<int> vec;
    for (int i = 0; i < n; ++i) {
      int num;
      cin >> num;
      vec.push_back(num);
      mx = max(mx, num);
    }
    int idx = -1;
    for (int i = 0; i < n; ++i) {
      if (vec[i] != mx) continue;
      if (i > 0 && vec[i - 1] < mx) idx = i + 1;
      if (i < n - 1 && vec[i + 1] < mx) idx = i + 1;
    }
    cout << idx << endl;
  }
  return 0;
}
