gropdf(1): Thick Lines

By default, gropdf(1) seems to set very thick lines.  Moreover,
linesize() global options in tables seem to be ignored unless the
line thickness has been set with a ‘\D't <whatever>'’ command
(the value of <whatever> doesn’t seem to matter) for linesize()
to kick into action.  This isn’t difficult, but the command
generates vertical space even when contained in a \Z'...' escape.
The only solution I’ve found is to put something like

.if '\*[.T]'pdf'  \{\
\Z@\D't -1'@
.  sp -(\n[PD]u+1)
.\}

into the file before the first call of SH (I’m obviously assuming
-man).  It works, but it’s kinda ugly; is there a cleaner way of
doing this that I’ve somehow failed to see?

Decades ago, I had similar issues with Elan Eroff.  But Eroff had
a simple solution: the ‘\D't...'’ escape set register ‘th’ to the
value in the escape; that register could be set to the desired
value at beginning of the file, with no addition of vertical
space.

I suspect this is happening in gropdf, but I’ve tried——without
success——to figure out just what’s causing it.  I’m running groff
1.23.0 on Windows.

This seems mighty similar to Ralph Corderoy’s comment on
2018-07-28; I’m not quite sure what the final resolution there was.

Jeff