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

def R(): return map(int, input().split())

def L(): return list(map(int, input().split()))

def I(): return int(input())

for _ in range(I()):
    n=I()

    a=L()

    m=max(a)

    if(m==min(a)):
        print('-1')
    else:
        for i in range(n):
            if a[i]!=m:
                continue

            if (i>0 and a[i]>a[i-1]) or (i<n-1 and a[i]>a[i+1]):
                print(i+1)
                break

