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 test in range(t):
    n=int(input())
    arr = list(map(int,input().split()))
    temp=arr[0]
    check=arr.count(temp)
    if check!=n:
        maxx=max(arr)
        for i in range(n):
            if arr[i]==maxx:
                if i-1>=0:
                    if arr[i-1]<arr[i]:
                        print(i+1)
                        break
                if i+1<=n-1:
                    if arr[i+1]<arr[i]:
                        print(i+1)
                        break
    else:
        print(-1)