without an actual example, enough information was given to address this question.
let's look at the definition shown in the question:
\par makes sure that processing is in vertical mode, necessary for the
to be applied in the proper direction.
two kerns are applied, one above and the other below the rule. all
instructions proceed downward in the vertical direction.
the amount of each kern is specified in terms of the
\baselineskip. for the
upper kern, this is the equivalent of two blank lines, and one line for the lower.
but it's not necessary to specify integral values -- distances can be expressed
with decimal values as well.
thus the obvious solution is to set the value of the lower kern to something
less than 1.
.5 is a reasonable place to start, and this can be adjusted by