The 8.9 system was incorrectly placing a 10.5 VDF font on the page rather than 9pt as requested by the input. Moving the 10.5pt font to the 2.4 system caused the 10.5pt font to be placed, even though it is in error. The correct behavior (in 2.4) is to place the 9pt font as requested by the input. The solution is to change the input to request the 10.5pt font and then have that font available as a virtual.
UPDATED: April 18, 2017