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:
        print(-1)
    else:
        p = max(a)
        for i in range(n):
            if a[i] == p:
                if i == 0 and a[i+1] < p:
                    print(i+1)
                    break
                elif i == n-1 and a[n-2] < p:
                    print(i+1)
                    break
                elif a[i+1] < p or a[i-1] < p and i != 0 and i != n-1 :
                    print(i+1)
                    break

