The fact that you physically see your corals' polyps taking in food would make me wonder what you're really seeing. When I touch my sps they retract their polyps as well. Did I just feed them? For all we know they are simply reacting with defense to the junk that was just poured in the water and will wait until it's diluted to take up its' nutrients as they break down.
When you touch your coral, you are generating a defensive reaction - the polyps of the whole colony, or nearly whole colony, retract almost in unison.
A coral feeding in the water column will have various polyps almost "gripping or grabbing" particulates out of the water, in a random assortment. And, usually, when, let's say a baby brine shrimp hits a tentacle, that tentacle will retract, followed by other tentacles of the same polyp - similar to what it would look like if you were to fold down your fingers one after the other when making a fist.
Now, if you tried to target feed a coral and blasted it with the turkey baster, then... yeah... you'll see a defensive reaction too....
In that study posted above, Dirk also fed one of his experimental tanks Nori Micro (some invert food found in Europe, I guess - I've never used it) and the other experimental tanks received a species of phytoplankton. And, obviously, the controls received nothing.
The A. tenuis in the tanks with the artemia (baby brine) all had significantly increased growth rates compared to the Nori micro, phytoplankton and controls.
Your sps coral are carnivorous. Don't feed them poo, don't wait for them to take it up across their membranes, or whatever. Maintain good water quality and feed them appropriate foods, along with your fish.
Cheers
Mike