I’m in favour of those scaling factors.
I use a scaling factor of 6 for 9x9 in my childrens club since 2012.
I used a scaling factor of 2 for 13x13 from 2012 until 2021, but it seemed a bit too easy for black relative to the handicaps on 9x9 and 19x19, so I increased that factor to 3 in 2021 and that seems to work better (better balance across different board sizes).