On my 28Z, not much air comes out of my most forward duct. This is simply because of too small of a duct running for too far of a distance.
The flexible duct they use is very air restrictive as it is not very smooth inside, so it really interrupts air flow. And some of it looks to be only about 2 1/2" in diameter, which is not going to move much air.
But its not the bathroom duct, so eventually the front of the coach will heat up.
We also take a small ceramic heater that we can also use to heat up the inside. I figure if I am at a campground, I'd rather use their electricity than my propane.
The only thing that works on a RV is the owner...