Trade income increases

Hi,

I was wondering whether increases in trade income are linear and whether there is any maximum level of trade increases. I've been building temples to Hermes to get increases in trade in cities close to my capital, Pella.

Does the increase give an extra fixed amount of mnai per citizen in the city?

Is there any ceiling to the trade bonus that a city can receive? For example, Athens has a wondrous temple of Hermes and a mercantile port and I'm currently building the wondrous music hall which provides a further increase in trade. Is it possible that I will get no additional income in respect of that increase as trade has already been maxed out in Athens?

Thanks in advance,

woirble

Pretty sure there isn't a cap.