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

input = sys.stdin.readline

def solve():
	n = int(input())
	al = list(map(int,input().split()))

	mx = []
	best = max(al)
	for i in range(n):
		if al[i]==best:
			if i>0 and al[i]>al[i-1]:
				print(i+1)
				return
			if i<n-1 and al[i]>al[i+1]:
				print(i+1)
				return

	print(-1)
	
def main():
	n = int(input())
	for i in range(n):
		solve()

main()