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())
    l = list(map(int, input().split()))
    k = max(l)
    f = 0
    for i in range (n):
        if l[i] != k:
            f = 1
            break
    if f == 1:
        z = -1
        for i in range (n):
            if l[i] == k:
                j = i
                while (j <= n - 1):
                    if l[j] != k:
                        z = j - 1
                        break
                    j += 1
                if z == -1:
                    j = i
                    while (j > -1):
                        if l[j] != k:
                            z = j + 1
                            break
                        j -= 1
            if z != -1:
                break
        print(z + 1)
    else:
        print(-1)