It is a cumulative effect. The more you add the more the reception is decreased. How much depends on what the company is providing. If the box you have is supplied by the company, they have jacked up your input to carry the box. You are just going to have to keep adding until it begins to affect your reception. I do not believe where you split makes any difference for CATV. Just remember unused ends are still using power. They sell special caps to close off unused cable ends. Did I miss anything????