Thank you, this clarifies things.
Also, while we are at it, the errata for the XXL (TO, p. 309) engine says something very confusing about Improved Jump Jets used with this type of the engine: "the heat modifiers for improved jump jet use and jumping with an XXL engine cancel each other out." I understood this as the heat for jumping doubles whenever the unit mounts an XXL engine, iJJ's or both. Other options would be unreasonable. It's just that the wording is really confusing.