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

for t in range(int(input())):
	n = int(input())
	a = [int(x) for x in input().split()]
	maxi, maxv, cd = 0, a[0], a[0] > a[1]
	for i in range(1,n):
		tmp = a[i] == maxv and not cd
		if a[i] > maxv or tmp:
			maxv = a[i]
			maxi = i
			tmp = i+1 < n and a[i] > a[i+1]
			cd = a[i] > a[i-1] or tmp
	if cd:
		print(maxi+1)
	else:
		print(-1)
