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 i in range(t):
    n=int(input())
    l=list(map(int,input().split()))
    m=max(l)
    mi=min(l)
    if(m==mi):
        print(-1)
    else:
        a=l.index(m)
        for i in range(a,n):
            if(i-1>=0 and i+1<n):
                if(l[i-1]<m or l[i+1]<m):
                    print(i+1)
                    break