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())
    ar = list(map(int, input().split()))
    if len(set(ar)) == 1:
        print("-1")
    else:
        m = max(ar)
        for i in range(len(ar)):
            if ar[i] == m:
                if i < len(ar) - 1:
                    if ar[i+1] < m:
                        print(i+1)
                        break
                if i > 0:
                    if ar[i-1] < m:
                        print(i+1)
                        break
