Number of mails to sync via "Load up to 25 more"

Account settings --> Fetching mail --> Local folder size sets the number of mails to fetch. Scrolling down in mailbox, you find Load up to 25 more, what let you fetch n x 25 more mails than stated in Local folder size.

Expected behavior

When I delete a mail, I expect it to be subtracted from the amount of mails added to Local folder size.
Say, I have Local folder size == 25. When I extend fetching to 200 mails via Load up to 25 more and delete 197 mails, I want the fetching to fall back to 25.

Actual behavior

Instead it continues the 200 mail synchronization until 197 new mails came in and kind of flushed the old ones out.

Steps to reproduce

See above.

Why this is important/annoying to me

I get lots of "spam" (not really important feedback of scripts). When I use Load up to 25 more several times to extend the fetching up to the last important mail and then delete the junk inbetween, it continues to fetch 200 mails, whats heavy on my data-bill and completely unnecessary since I know the older ones.

Environment

K-9 Mail version: 5.203

Android version: 7.1.1

Account type (IMAP, POP3, WebDAV/Exchange): IMAP

Reproduce the issue in Account settings > Fetching mail > Local folder size using an IMAP account, then extend fetching with “Load up to 25 more” and delete the fetched messages. Trace the synchronization behavior responsible for the local folder limit; done means deleting messages reduces the effective fetch count and the app returns to the configured limit.