For example, with stock Russian dictionary:
Межгала*т*тическую -> Межгалактическ*ий* (!), *Вне*галактическую (!!), etc.
мес><ные -> *при*месные, *мало*весные
In both cases correct variants aren't EVEN offered!
As you see, even TRIVIAL misspellings of 1 misspelled or missed letter FAIL to give correct suggestion. It's UNACCEPTABLE.
I don't know which russian dictionary you are using, but you should contact russian dictionary maintainer(s), for the LibreOffice developers don't work on dictionaries. This is external stuff.
Spelling suggestions are made by Hunspell, so you should read the documentation to help to improve it if you can:
Use the command REP and TRY, which are not really used in the russian dictionary in which I had a look.