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 _ in range(int(input())):
	n = int(input())
	a = list(map(int,input().split()))
	m = max(a)
	if len(set(a))==1: print(-1)
	elif a[0]==m and a[1]<m: print(1)
	elif a[-1]==m and a[-2]<m: print(n)
	else:
		for i in range(1,n-1):
			if a[i]==m and (a[i-1]<m or a[i+1]<m): print(i+1);break