I haven't read all of the book yet. Discussion of the Invercone appears to be spread throughout the book. My first impression is that they may see the Invercone as having a cardioid response pattern, but that's not based on a complete reading.
Originally Posted by Steve Smith
It's a new book to me. I'd heard of it, but haven't seen it locally available or widely discussed in the US. My hardback 1981 copy was ordered through abebooks for US$1 and US$2.99 shipping. It appears to be technically very solid, although a bit dated in areas where some equipment is concerned, but it is based on a 1952 edition with revisions until at least 1981. Well worth a read. They do discuss under what conditions it's necessary to depart from standard metering techniques, and what methods of departure are effective.