> Any further comments on this issue would be greatly appreciated.

There are two separate aspects:

1. It is required that the database file is accessed by an single
instance of firebird server only.

As soon as there are multiple instances accessing the same file it will
result in garbage.

2. It is an good idea to have server instance and database file on the
same physical machine.

By default firebird does try to enforce that. But, there are config
options to allow remote files.

Using an remote file does definitely slow down processing sonce no
networking is as fast as an local disk.

It might also lower stability since an network connection is not as
stable as the connection to local disk.

Elmar