Not an exact answer to the question, but maybe another solution to the problem.
Try the "identifier dictionary" . You may have to install the package "Cody". Then it is in the "Source" menu. (towards the bottom "Show Unit/Identifier dictionary")
You can assign it to keyboard too.
Normal code completion, only works, if
- you know the *start* of the identifier you are looking for
- the unit is already in the uses
"identifier dictionary" searches all units, and it can search for any part in the middle of a name