How have courts interpreted the doctrine of heat-of-passion manslaughter in the context of imperfect self-defense?

In People v. Flannel (1979) 25 Cal.3d 668, 160 Cal.Rptr. 84, 603 P.2d 1 (Flannel), we approved the reasoning of Best, expressly adopting imperfect self-defense as a category of voluntary manslaughter (Flannel, at pp. 675-676, 160 Cal.Rptr. 84, 603 P.2d 1), but we disconnected it from heat-of-passion manslaughter (id. at pp. 677-678, 160 Cal.Rptr. 84, 603 P.2d 1). We separated these doctrines because imperfect self-defense by definition involves an unreasonable response to the circumstances (for otherwise it would be true self-defense), whereas heat-of-passion manslaughter requires a provocation that would arouse the passions of a "`reasonable person.'" (Id. at p. 678, 160 Cal.Rptr. 84, 603 P.2d 1, italics added.) We believed these standards to be mutually inconsistent. (Ibid.) We did not, however, recognize that even in the case of heat-of-passion manslaughter (where the defendant's passion must, by definition, be reasonable), the defendant's conduct is certainly unreasonable in the sense that manslaughter constitutes a serious crime, not an exculpation. Therefore, the reasonableness component of heat-of-passion manslaughter has always managed to coexist with the recognition that we are talking about a defendant who has acted unreasonably.