1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

import math
from collections import deque
from sys import stdin, stdout, setrecursionlimit
from string import ascii_letters
letters = ascii_letters[:26]
from collections import defaultdict
#from functools import reduce
input = stdin.readline
#print = stdout.write
 
for _ in range(int(input())):
    n = int(input())
    arr = list(map(int, input().split()))
    mn = min(arr)
    mx = max(arr)
    if mn == mx:
        print(-1)
        continue
    was = False
    for i in range(n):
        if arr[i] == mx and (i > 0 and arr[i - 1] < mx or i < n - 1 and arr[i + 1] < mx):
            print(i + 1)
            was = True
            break
    if not was:
        print(-1)
    