Here are the acceptance rates for different intended concentrations (coming out of the litigation data prior to 2015):
CS/Eng 4.4% < Bio Science 5.2% < Social Sci 5.9% < Physical Sci 6.2% < Undecided 6.3% < math 6.9% < humanities 7.4%
In the last few years the number of CS/Eng applicants keeps rising. Given the fact that yield is typically inversely related to acceptance rate and Harvard’s average yield is 82%, I imagine yield from CS/Eng admits could be north of 85%. That means that Harvard is likely to win over 80% CS/Eng cross-admits.
The low rate for CS/Eng could either be due to yield protection (Tufts syndrome) or a cultural protection—Harvard doesn’t want too many engineers to change the feel of College. I suspect its the latter. As Fitzsimmon put it Harvard wanted more “humanists”.