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())
    l=list(map(int,input().split()))
    m=l[0]
    ind=1
    flag=0
    for i in range(len(l)):
        if(l[i]!=m):
            flag=1
        if(l[i]>m):
            m=max(m,l[i])
            ind=i+1
        if(l[i]<m and i!=0 and l[i-1]==m):
            ind=i
    if(flag==0):
        print(-1)
    else:
        print(ind)