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 i in range(int(input())):
	n = int(input())
	arr = list(map(int,input().split()))
	if len(set(arr))==1:
		print(-1)
	else:
		mx = max(arr)
		if arr[0]==mx and arr[0]>arr[1]:
			idx = 1
		if arr[n-1]==mx and arr[n-1]>arr[n-2]:
			idx = n
		for i in range(1,n-1):
			if arr[i]==mx and (arr[i]>arr[i-1] or arr[i]>arr[i+1]):
				idx=i+1

		print(idx)