What are the most reliable ports to use for FIX API?

Please can someone advise what ports I should use to connect to FIX API? I currently use h6.p.ctrader.com for one of my systems which seems stable, but I need to add another system to the same account and tried using h5.p.ctrader.com, but this has failed several times.

Should I be using a port that does not get used elsewhere, such as cTrader web app, or should I be using the ports as dynamically displayed in the cTrader FIX connection window (which changes constantly!)