For the GenericAutocompleteSearchTemplateDynSelect_line template of a dynSelect the "templateOptions" support "keyFieldWidth" setting (default value is 280), that allows you to set the dynSelect Key field width using the "templateOptions" attribute.
Example:
Template: GenericAutocompleteSearchTemplateDynSelect_line
templateOptions: fa fa-user|contactdesc|contactdesc#KeyFieldWidth=220
