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

from math import *

sInt = lambda: int(input())
mInt = lambda: map(int, input().split())
lInt = lambda: list(map(int, input().split()))

t = sInt()

for _ in range(t):

    n = sInt()
    a = lInt()
    if max(a) == min(a):
        print(-1)
    else:
        max_ = max(a)
        for i, al in enumerate(a):
            if al != max_:
                continue
            if i == 0:
                if a[i] > a[i + 1]:
                    print(i + 1)
                    break
            elif i == n - 1:
                if a[i] > a[i - 1]:
                    print(i + 1)
                    break
            else:
                if a[i] > a[i - 1] or a[i] > a[i + 1]:
                    print(i + 1)
                    break

























