\magnifyMusic omits unison notes in \partcombine?

[Karlin High]

A songwriter looked at my LilyPond job and asked, "Can you make the note 
heads bigger in proportion to everything else?" Yes, thanks to 
\magnifyMusic, I thought. It's a SATB hymn, I'm using \partcombine, and 
apparently \magnifyMusic doesn't pick up the unison notes the way I'm 
writing it. Minimal example below, PNG result attached. Magnify is at 
1.2 for effect; I'm using 1.1 in practice.

% BEGIN LILYPOND CODE
\version "2.19.59"
one = { a'2 f' }
two = { f'2 f' }
\partcombine #'(2 . 9) \magnifyMusic 1.2 { \one } \magnifyMusic 1.2 { \two }
% END LILYPOND CODE

I've found I need to put \magnifyMusic inside \partcombine, because it 
seems to have no effect the other way around. Any ideas for how I could 
get \magnifyMusic to catch the unison notes?
--
Karlin High
Missouri, USA

MagnifyPartCombine.png
Description: MagnifyPartCombine.png