How to set width of a Salesforce Docusign merge field anchor tag without having to resize manually every time

I’ve created a merge field in Docusign that is to write back to an opportunity field in Salesforce, and have placed the anchor tag in my word document template.  When I go to send the document out for signature, the text field for data to be entered is barely wide enough to notice it’s even there:

I know I can manually adjust the width of the field before sending, but asking my users to have to do this for every contract that goes out is not reasonable.  How can I set this anchored merge field to be wider by default?