WordPress acts like it's installed in root, when it's actually in a subdirectory

I tried posting this several days ago but didn’t get any responses — and I’m afraid it’s because I was far too wordy and confusing in the way I first tried to ask it. So I’m hoping I can try again. ??

Essentially, I have WordPress installed in a subdirectory (at freeish.net/msp/), but WordPress is acting like it’s actually installed at the root level. So it wants to create permalinks like “http://freeish.net/sample-post/” rather than like “http://freeish.net/msp/sample-post/” — which is what I want it to do.

The index.php file is indeed in the /msp/ folder, as it should be, and the .htaccess file contains the following rewrite code:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /msp/
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /msp/index.php [L]
</IfModule>
# END WordPress

Note: when WordPress creates this URL rewrite code for itself, it always creates it without “/msp/” in either of the locations where you’ll see it above. Without “/msp/” on either the RewriteBase or RewriteRule lines, however, all links on the site end in 404 errors. But if I manually add “/msp/” in these two places in the .htaccess file, then permalinks work okay — albeit at the root level (i.e., freeish.net/sample-post/).

So here’s the question:
How do I force WordPress to create permalinks in the subdirectory where WordPress is actually installed?

Thanks very much in advance!