When properties such as hst:showcontextpath, hst:showmount, hst:scheme etc. are placed on the mount below /hst:platform, they have no effect.
Let's make that visible to developers, e.g. by WARN log statement.
Note that they are typically on the top level host node, see https://documentation.bloomreach.com/14/library/concepts/hst-configuration-model/hosts-configuration.html
As a client puts it:
What is documented is that you CAN set them higher IF you want them to "cascade", not that you MUST.
The other thing is that these properties work perfectly FINE when set directly on the mount in the SITE hosts.
Basically, the hosts for SITE and platform have the same node types and properties, but they behave entirely differently. At the very least, that's a bad "user" experience.