Polymetric math

[David Santamauro]

Hi,
I’m typesetting an ensemble piece in 4/4 where one instrument goes to 6/4 – 
basically short-hand for not having to write two groups of quarter note triples 
for a longer duration. If I follow the documentation, it should be (according 
to the math): 2/3 * 6/4 = 12/12 (4/4). But the following doesn’t work:

\version "2.22.2"

\include "english.ly"

\relative <<
  \new Staff {
    \time 4/4
    c'4 c c c |
    c4  c c c  |
  }
  \new Staff {
    \time 4/4
    \set Staff.timeSignatureFraction = 6/4
    \scaleDurations 2/3
    c4 c c c c c
  }
>>

This is my first sojourn into polymetrics with lilpond, so any rudimentary help 
would be appreciated.

Thanks