One thing I noticed is when both the flounder and striper are feeding on the surface baits, they grab the bait and turn rapidly. When feeding in the water column or near the bottom they inhale the bait and stay put.
I've seen flounder swimming in the lights under the pier and have also seen them come out of the water chasing mullet.
There was one day in late August at least 4 or 5 years ago when a huge school of flounder had peanuts pinned up against the inlet side of the Longport jetty. There were at least 15-20 guys on the jetty and most of them were hooked up all at once for about 2 hours. They hit anything you threw at them. Most of the fish were sub legal but there were enough keepers to make it interesting. I had no idea flounder were that ravenous until I experienced the flounder blitz that day. From that day on I realized that flounder are NOT a lazy bottom fish like everyone thinks.