With the double non-fouler mod, it is 100% sealed and there are absolutely no leaks.

Here are the 2 non-foulers on the sensor:


Here it is on the manifold:


As exhaust gas rushes past, the only hole the exhaust gases go by is the hole in the bottom of the non-fouler that is plugged into the manifold. Past that hole, there is the opening of the 1st non-fouler with the tip of the o2 sensor and past that, it is 100% totally sealed. There are zero leaks.

Maybe I misunderstood the comments, but the unit is sealed so based on this, there should be low pressure around the o2 sensor probe.

As far as any effects, I'm just thinking that the exhaust gases rushing past will not be able to really push any oxygen into there since the exhaust gas rushing past will suck anything out of the sealed chamber further reducing the chance of the sensor reading any oxygen at all.