Customise form sets data field to varchar(140) no matter what. How do I fix?


I am trying to add fields to an invoice but am hitting the mysql data table maximum size. I checked in the table and all select and data fields have a varchar(140) length assigned. I can’t set a size in customise sales invoice. I’m using Erpnext 11. Where can I find the core code that sets this ridiculously high figure so I can get it to behave and actually use the length I try to enter. ie 3 characters, or 11 etc. Its terrible that a Select Yes/No field is 140 characters long and not three.
This is now causing me much grief in the Sales Invoice as I require quite a few extra fields due to compliance both gas and electrical.

Any help would be appreciated.