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())
while t:
    t -= 1
    n = int(input())
    a = list(map(int, input().split()))
    maxi = max(a)
    ans = None
    if len(set(a)) == 1:
        print(-1)
    else:
        for i in range(n):
            if a[i] == maxi:
                if i > 0 and a[i-1] < maxi:
                    ans = i+1
                    break
                if i < n-1 and a[i+1] < maxi:
                    ans = i+1
                    break
        print(ans)