"Create Geospatial PDF" makes PDF dimensions much larger

I am using QGIS 3.10.9-A. When I use Export as PDF... and check the Create Geospatial PDF (GeoPDF) box the size (linear – not number of bytes) of the PDF created is much larger than the desired paper size. This happens even if the layout is simply a blank sheet of paper. If I make another PDF without checking the Geospatial PDF option the size is the same as desired paper size.

For example, if I specify the layout to be on Letter-size (11 x 8.5 inches) paper and then open the PDF in Adobe Acrobat, the "Document:" dimensions shown in Acrobat when preparing to print with page scaling set to None are 45.8 x 35.4 inches, 4.16 times the paper size.

I can print the PDF on Letter-size paper using page scaling set to Fit to Printable Area or Shrink to Printable Area (both show a Zoom of 23%) but to print to accurate scale I prefer to set page scaling to None. Also, if combining PDFs of QGIS layouts with PDFs from, say, MS Word, the reader will have to rescale to read.

Any suggestions?