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 _ in range(t):
    n = int(input())

    arr = list(map(int,input().split()))

    sss = list(set(arr))
    sss.sort()
    # print((arr))

    if(len(sss) == 1):
        print("-1")
    else:
        vvv = sss[len(sss)-1]
        # print(vvv)
        ans =-1
        for i in range(n):
            if(arr[i] == vvv):
                if(i >0 and arr[i] > arr[i-1]):
                    ans = i+1
                    break
                elif(i<n-1 and arr[i] > arr[i+1]):
                    ans = i+1
                    break

        print(ans)
