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 program():
    notdomi=set()

    n=int(input())
    l=list(map(int, input().split()))

    m=max(l)

    for i in range(n):
        if l[i]==m:
            if i!=0:
                if l[i-1]!=m:
                    print(i+1)
                    return

            if i!=n-1:
                if l[i+1]!=m:
                    print(i+1)
                    return


    print(-1)


for i in range(int(input())):
    program()

"""
5 5 3 4 4 5



"""