I’ve given up on trying to have Aspell working for this use case. Even by having a conf file in place, and by tweaking around with the list option, and the boolean option, it didn’t work.
As far as I can tell, and going by the Aspell Customizing suggestion that appears on the documentation page, there is no possible way to go around this issue.
What I do have in place and which seems to work for now is with Hunspell on the spell.kak file instead.