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 j in range(t):
    a = 0
    n = int(input())
    A = list(map(int, input().split()))
    m = max(A)
    if len(set(A)) == 1:
        print(-1)
    else:
        for i in range(len(A)):
            if A[i] == m:
                if i > 0 and A[i-1] < m:
                    print(i+1)
                    break
                elif i < (len(A)-1) and A[i+1] < m:
                    print(i+1)
                    break
