Results of GetTextExtentPoint32 aren't scaling linearly with nHeight - vba

Question

I've written a VBA function to return the width of a string in a given font & point size at 300dpi. I'm not a very experienced programmer, and this is my first use of Windows API. I would expect the width to decrease gradually with font size, but its not so gradual.
For example:
Point Size = Returned Width (string "Text" in font Arial)
14 = 99
13.5 = 95
13 = 91
12.5 = 90
12 = 84
11.5 = 83
11 = 75
So reducing font size by 0.5 changes width by 4>4>1>6>1>8. I'd like to understand why there's a non-linear relationship between font size and returned width. I know there's vaguery in font rendering, but I'd guess that's not the whole story here, especially not at 300dpi?
Like I said, I'm a not-quite-novice so feel free to say "Google [keyword], scrub!"
Context: Unlike most uses of GetTextExtent, there is no object I'm trying to fit. End goal is a function to return whether string A at X points is wider than string B at Y points when printed in font F at 300dpi.
Here's my code collapsed to one function...
Option Explicit
Private Declare PtrSafe Function CreateDC Lib "gdi32.dll" Alias "CreateDCA" (ByVal lpDriverName As String, ByVal lpDeviceName As String, ByVal lpOutput As String, ByVal lpInitData As Long) As Long
Private Declare PtrSafe Function CreateFont Lib "gdi32.dll" Alias "CreateFontA" (ByVal nHeight As Integer, ByVal nWidth As Integer, ByVal nEscapement As Integer, ByVal nOrientation As Integer, ByVal fnWeight As Integer, ByVal fdwItalic As Long, ByVal fdwUnderline As Long, ByVal fdwStrikeOut As Long, ByVal fdwCharSet As Long, ByVal fdwOutputPrecision As Long, ByVal fdwClipPrecision As Long, ByVal fdwQuality As Long, ByVal fdwPitchAndFamily As Long, ByVal lpszFace As String) As Long
Private Declare PtrSafe Function SelectObject Lib "gdi32.dll" (ByVal hDC As Long, ByVal hObject As Long) As Long
Private Declare PtrSafe Function GetTextExtentPoint32 Lib "gdi32.dll" Alias "GetTextExtentPoint32A" (ByVal hDC As Long, ByVal lpctStr As String, ByVal c As Integer, ByRef sz As SIZE) As Boolean
Private Declare PtrSafe Function DeleteDC Lib "gdi32.dll" (ByVal hDC As Long) As Long
Private Declare PtrSafe Function DeleteObject Lib "gdi32.dll" (ByVal hObject As Long) As Long
Private Type SIZE
x As Long
y As Long
End Type
Function GetPrintedWidth(strToTest As String, strFontName as String, sngFontSize As Single)
'Create the device context. (Documents are rendered to PDF before printing, so I'm using the Adobe PDF printer driver. Mistake?)
Dim DC As Long: DC = CreateDC(0, "Adobe PDF", 0, 0)
'Convert sngFontSize points to logical units. Final print is #300dpi.
'Most examples I've seen use MulDiv, but it converts sngFontSize to long before calculating.
Dim nHeight As Long: nHeight = sngFontSize * 300 / 72
'Create the font.
Dim fnt As Long: fnt = CreateFont(nHeight, 0, 0, 0, 400, 0, 0, 0, 0, 0, 0, 0, 0, strFontName & Chr$(0))
'Select font into DC.
DeleteObject SelectObject(DC, fnt)
'Get string dimensions.
Dim sz As SIZE: GetTextExtentPoint32 DC, strToTest, Len(strToTest), sz
'Return width.
GetPrintedWidth = sz.x
'Clean up.
DeleteObject fnt
DeleteDC DC
End Function
I'm extremely open to basic code corrections, I'm still learning!
Y'all are the best, thanks for everything :)
Update
Increasing nHeight smooths things out. I get nearly linear results going from:
nHeight = sngFontSize * 300 / 72
to:
nHeight = sngFontSize * 3000 / 72
So... I guess it is just a font scaling issue, but I'm completely in the dark as to why. AFAIK the nHeight formula should be
FontSize * PointsPerLogicalInch / 72
...ergo a 300dpi printer should have 300 PointsPerLogicalInch, no?
Update 2
GetDeviceCaps LOGPIXELSY is usually used to get PointsPerLogicalInch. I tested my available printers:
Adobe PDF print driver returned 1200
My desk printer returned 600
Incidentally, LOGPIXELSX returned the same
So 300 should be right or I've bungled something.