It will be interesting if Ross experiments with vent tube angles. I have never heard of anyone doing this before. One idea I had was to put a short length of some soft bendable tubing like copper over the end of the cap vent steel tubes (tight fit with good seal) to be able to try many different angles without work hardening the steel tubes. I might try this myself one of these days, just to try to verify the cause, not because of any worries.