Still don't understand how counter pressure filler works

OK, so you slowly fill the bottle up releasing a little pressure until it foams over.  Then I have foam in the top half to third of the bottle.  I quickly cap it, but won't the haed space eventually even out and reduce the overall pressure making the beer kind of flat?  Or do you let it foam over until the liquid level is almost to the top?

What to you experts say?

If the bottle is pressurized, & you fill by letting out gas, you should be able to get the bottle almost full.  The counter pressure keeps the foam down.  Practice makes perfect? 

Sorry that's all I've got.

The best use of a CP filler will equalize the pressure between the bottle and the keg. Then gravity moves the beer into the bottle as the gas goes back into the keg, or is slowly vented from the bottle.

If you're releasing pressure and getting foam, then the two are not at equalibrium. The foam is robbing you of carbonation and head retention.

In almost all cases, you will find that filling goes smoother if the keg is above the bottle.

I just filled up some bottles yesterday for the first time, worked great.  Make sure you have a tight fit at the cork on the bottle, open just the gas then open the bleeder just a little to bleed out the air and fill with CO2.  Now shut off the bleeder and pressurize the bottle, shut the gas valve and open the beer valve not much should happen if everything is right.  Now open the bleed valve just a little and you should see the beer entering the bottle from the bottom with no foam let it fill slowly until you start to mush beer out the vent close the beer valve and the vent valve, remove the filler and cap.  I only got a little foam in each bottle but just pushed it out the vent.  I think it was when I opened the gas valve on a new bottle it pushed the beer out that was left over in the filler from the previous bottle. 

You need to fill the bottle at least up to the neck or even further, if you can manage. If you only fill the bottle to half full you will get a flat beer as you need to de-pressurise before capping and then will lose lots of CO2 to the empty space as it re-pressurises. If you're getting that much foam then you're either filling up too quickly or the beer is too warm, possibly a combination of both.

Cheers,

Vale