Alto has this problem right from the factory.
And it lies in the Brake Master Cylinder ! It doesnt provide enough vaccum to handle braking.
The only way you can get better braking performance is to Swap the Master Cylinder with one from the Cultus. A new one costs around 4k (not confirmed, confirm kar lo frm spare parts shop) and used ones are cheaper. And pay 500 to the mechanic for installation.
Cheerz!