No Ron your are incorrect, gasses push back down the bore equally all the way around the bore. The as the gasses come back down the bore and encounter the cone their angle of incidence is changed from straight back and down then deflected into or towards the flash channel. With the cone the gas pressure is deflected to the side of the bore or breech plug and back across the cone to the other wall. In effect reducing some of the back pressure passing back through the flash channel. There was a drawing created by a math guy that showed the reaction but I am unable to find it now.

But I think if you visualize the normal flash hole construction on the powder side, the area of the flash hole is usually an inverted cone allowing a small portion the powder to come closer to the flash hole or even a flat flash hole. With ignition those same blow back gasses react straight back to the inverted cone and down the sides of the cone to the flash hole.

Turning the cone over creates the opposite movement.

Example take a cone - invert it and pour water in it where does the water tend to go? Then take the cone and place the point up and pour water on it just the opposite happens water is deflected away from the center of the cone. It only last for a moment in an enclosed tube before the water/pressure builds up enough that it essentially over flows and then does go back through the flash channel. But as soon as the bullet exits the barrel it creates the opposite reaction and sucks the bore out. I know it is a stupid simple simulation but the easiest way I can think of to explain it. If I could find the drawing and simulation the math guy did - it makes much more sense.

One other point when I was rebuilding breech plugs and testing the effect, at that time by reading the shot primer you could see the differences in the flow of the primer created by pressure around the hammer imprint in the expended primer with identical loads of powder and bullet. There was a DIFFERENCE