Great news! The newest patch now defaults to 1/4" scale when adding drawings to a Planset page.
Thanks SoftPlan!
Release: 2020.2.6
Feature: Default Planset Scale
Description: If the space available on a planset page will allow for an inserted drawing 1/4 inch scale, the drawing will now be inserted at 1/4 inch. It will use 1/4 regardless of whether a larger scale will fit.