Lets say you have 5 planets with only one phase lane connection each one to the next (like a string of pearls).  Obviously, putting a Trade Port at the two planets on the ends will generate the most income.  But what happens if you place a trade port in any of the planets in the middle?  Will they generate income as well?  Will the trade ship stop at one of the middle ones and reduce the credits earned because he had a shorter trip?  What about putting multiple trade ports at the same planet?  Like if I have this one really remote planet, will filling up all its logistics slots with Trade Ports multiply my trade income by each additional port?  Or will the trade ships just fly inbetween the ports in that gravity well and basically make me no money? 

Essentially, I want to know what is the most effective way of utilizing Trade Ports.