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

t=int(input())
for i in range(t):
    n=int(input())
    a=[int(a) for a in input().split()]
    b=max(a)
    if b==min(a):
        print(-1)
    else:
        if b == a[0] and a[0] > a[1]:
            print(1)
        elif b==a[n-1] and a[n-1]>a[n-2]:
            print(n)
        else:
            for j in range(1, n-1):
                if b==a[j] and (a[j]>a[j+1] or a[j]>a[j-1]):
                    print(j+1)
                    break