Yes, Robert and Tim are correct. The extra tree wastes metal and adds no benefit to casting. The Vacuum vent, the way you have it helps the wax tree melt out quickly as it opens up a channel for the air to come in as the wax melts out.As a side effect, that might help suck out the debris from the resin a tiny bit as your pieces all drain in the correct direction
Vacuum vents work best if directly attached to the top of the pieces or to areas that have no drainage.
That being said, you should try casting without a Vacuum vent to see if you get any difference.You might not need it due to the shape and size of your designs.
Your designs are much easier to evacuate as they are long and everything points/ drains to the base. That explains why you have no problems casting some of the other resins and why you have very little residue if any.
When you look at other designs that do not drain / burn away easily due to long sections going across from one side to the other or heavy complex items with engraving or raised lettering and areas that act as a "trap" for the resin ...thats where the Vacuum vent really helps. Put the vent near or on one of those areas and it is a big help.
In the case of a section not being able to drain correctly, thats where the very high burn out can help 1400 oF and higher as some people are doing.
I guess that was more then 2 cents