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())
    L=list(map(int,input().split()))
    M=max(L)
    m=min(L)
    #print(N,M,L)
    if M==m:
        print(-1)
    else:
        L=[M]+L+[M]
        #print(L)
        for i in range(1,N+1):
            if L[i]==M:
                if L[i]>L[i-1] or L[i]>L[i+1]:
                    print(i)
                    break
                