Problems with page layout dimensions in the memoir class

Recently, when defining the layout geometry for my doctoral thesis, I faced the following problem: the dimensions informed by me, which I will call virtual dimensions, do not correspond to the dimensions of the paper, which I will call the real dimension.

In the composition of my thesis, I opted for the memoir class, because I consider it to be a class composed of many resources and, for this very reason, very versatile. Reading the class manual, I found on page xxxv, where the author defines the terminology to be used, that the conversions used by the class are 72.27 pt for each 1 in, which corresponds to 25.4 mm. However, when I bring this to the real paper, (that is, after printing the data on the sheet of paper) and checking the dimensions with a ruler, I see that these values ​​do not match.

My intention was always to use the A4 paper format and, for this reason, I chose the class option a4paper, but when I found the conflict between the virtual and real dimensions, I decided to use the internal configuration commands and typed the following code:

documentclass[12pt,a4paper,extrafontsizes,showtrims]{memoir}
usepackage[english,brazil]{babel}
usepackage{lipsum}

setstocksize{297mm}{210mm}%
settrimmedsize{stockheight}{stockwidth}{*}
settrims{0mm}{0mm}
setlrmarginsandblock{30mm}{20mm}{*}%
setulmarginsandblock{30mm}{20mm}{*}%
setheadfoot{baselineskip}{2baselineskip}
setheaderspaces{20.0mm}{*}{*}%
setmarginnotes{2.0mm}{16mm}{5.0mm} setcolsepandrule{3.5mm}{0.15mm}
setfootins{bigskipamount}{bigskipamount}
checkandfixthelayout[fixed]

begin{document}
lipsum
end{document}

After printing on the sheet of paper, I took some measures and noted them in the following table:

In the first column, I wrote down the measured items. In the second and third columns, I annotated the real values (which I would like to obtain) and virtual values (values ​​truly obtained despite the values informed in the code), respectively. In the fourth column, I annotated the ratio between the real and virtual values, and in the fifth column, I annotated the corrected value (the value entered the code multiplied by the correction factor).

In the face of all this exhaustive narrative, what I would like to know is whether anyone has encountered this problem before, and how it could be resolved.

% mempageprob.tex  SE 554615
documentclass[12pt,a4paper,extrafontsizes,showtrims]{memoir}
usepackage[english,brazil]{babel}
usepackage{lipsum}
usepackage{layouts}

setstocksize{297mm}{210mm}%
settrimmedsize{stockheight}{stockwidth}{*}
settrims{0mm}{0mm}
setlrmarginsandblock{30mm}{20mm}{*}%
setulmarginsandblock{30mm}{20mm}{*}%
setheadfoot{baselineskip}{2baselineskip}
setheaderspaces{20.0mm}{*}{*}%
setmarginnotes{2.0mm}{16mm}{5.0mm} setcolsepandrule{3.5mm}{0.15mm}
setfootins{bigskipamount}{bigskipamount}
checkandfixthelayout[fixed]

begin{document}

begin{figure}
currentpage
oddpagelayouttrue
pagedesign
caption{Odd page layout for this document}
end{figure}

rule{15cm}{5mm}

lipsum
end{document}