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

for _ in range(int(input())):
    x = int(input())
    l = list(map(int,input().split()))
    m = l.index(max(l))
    ans = 0
    bool = False
    for num in range(x):
        if m - 1 in range(x):
            if (l[m-1] < l[m]):
                ans = m+1
                bool = True
                break
            elif m + 1 in range(x) and l[m+1] < l[m]:
                ans = m + 1
                bool = True
                break
            else:
                m += 1
        else:
            if m + 1 in range(x):
                if l[m+1] < l[m]:
                    ans = m+1
                    bool = True
                    break
                else:
                    m += 1
    if len(l) == 1:
        print(1)
    elif bool:
        print(ans)
    else:
        print(-1)