At the start of a campaign at FB I tend to bid high to get some traffic and let the ctr pull my cpc down but after few days it looks like facebook shows my ad again and again to the same people, bringing the frequency up.
When should I really put the cap on CPC ? is it good to just reduce the cpc after you drove couple hundred clicks with high ctr and cpc being already low ?
You can't do nothing about it. Make more new ads, and move on.
It's getting harder even with high ctr% pics, but yes you can lower your cpc, if you clic to change it you'll notice the suggested bid has changed and is normally adjusted to your ctr% , mas o menos.
Mehdi