The maxtype controls the database column type that gets defined. ALN/UPPER/LOWER for example are defined as varchar2 on Oracle which has a database limitation of 4000 bytes. You would need to have a maxtype of CLOB to essentially support an unlimited size of characters.
I would personally never define a field that large on a table that is used for other purposes like the WORKORDER, ASSET, etc. table. I would configure a shorter (100-400 character, not even 4000) description field to act as a summary and then enable that field to have its own long description that would get referenced as a non-persistent attribute on the core table (WORKORDER, ASSET, etc.) and then persistently stored in the longdescription table.