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())):
    n = int(input())
    a = list(map(int, input().split()))

    if len(set(a)) == 1:
        ans = -1

    else:
        max_val = max(a)

        for i, val in enumerate(a):
            if val == max_val:
                if i == 0:
                    if val > a[1]:
                        ans = i + 1
                        break

                elif i == n-1:
                    if val > a[-2]:
                        ans = i + 1
                        break

                else:
                    if a[i-1] < val or val > a[i+1]:
                        ans = i + 1
                        break

    print(ans)