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 sys
import math
from math import *
from collections import Counter,defaultdict,deque
from bisect import bisect
    
lip = lambda : list(map(int, input().split()))
ip = lambda : int(input())
sip = lambda : input().split()
mod = 10**9+7
	

def main():
	n = ip()
	arr = lip()
	mx = max(arr)
	
	for i in range(n):
		if mx == arr[i]:
			if i == 0:
				if arr[i] > arr[i+1]:
					print(i+1)
					return
			elif i == n-1:
				if arr[i] > arr[i-1]:
					print(i+1)
					return 
			else:
				if arr[i-1] < arr[i] or arr[i]>arr[i+1]:
					print(i+1)
					return
	print(-1)


for i in range(ip()):
	main()
