Can't set different font sizes for labels in QGIS

Question

I use the Easy Custom Labeling plugin to draw lines along which inscriptions are placed (curves). The font size is set by itself, although I set certain parameters, and the size is displayed as it turns out. The expression that I used:

CASE
 WHEN "UN subreg" =  'Antarctica'  THEN 30 
    WHEN "UN subreg" =    'Eastern Asia'    THEN 30
    WHEN "UN subreg" =    'Eastern Europe'   THEN 30
    WHEN "UN subreg" =    'South America'    THEN 30
     WHEN "UN subreg" =  'Caribbean'  THEN 24
     WHEN "UN subreg" =  'Central America'   THEN 24
    WHEN "UN subreg" =   'Australia and New Zealand'   THEN 24
    WHEN "UN subreg" =    'Central Asia'    THEN 24
    WHEN "UN subreg" =    'Eastern Africa'    THEN 24
    WHEN "UN subreg" =    'Melanesia'    THEN 24
    WHEN "UN subreg" =    'Micronesia'    THEN 24
    WHEN "UN subreg" =    'Middle Africa'    THEN 24
    WHEN "UN subreg" =    'Northern Africa'    THEN 24
    WHEN "UN subreg" =    'Northern Europe'    THEN 24
    WHEN "UN subreg" =    'Polynesia'    THEN 24
    WHEN "UN subreg" =    'South-Eastern Asia'    THEN 24
    WHEN "UN subreg" =    'Southern Africa'    THEN 24
    WHEN "UN subreg" =    'Southern Asia'    THEN 24
    WHEN "UN subreg" =    'Southern Europe'    THEN 20
    WHEN "UN subreg" =    'Western Africa'    THEN 24
    WHEN "UN subreg" =    'Western Asia'    THEN 24
    WHEN "UN subreg" =    'Western Europe'    THEN 20
    END

And what I get.

Sometimes, when I change the font size for some labels, all labels or some parts of them become too small or too big. I use the QGIS 3.28.11 version.