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 i in range (t):
    n = int (input())
    a = [int(i) for i in input().split(" ")]
    m = max(a)
    ans = -2
    for j in range(n):
        if a[j]==m and j>0 and a[j]> a [j-1]:
            ans = j
        if a[j]==m and j < n -1 and a[j]> a [j+1]:
            ans = j
    print(ans + 1)
