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 _ in range(t):
    n=int(input())
    arr=list(map(int,input().split()))
    
    x=max(arr)

    q=list(set(arr))
    # print(q,len(q))
    if len(q)==1:
        print(-1)
    else:
        # arr.index(x)
        if arr[0]==x and arr[1]!=x:
            print(1)
        else:
            for i in range(1,n):
                if arr[i]==x and (arr[i-1]!=x or arr[i+1]!=x):
                    break

            print(i+1)
    