SharePoint view columns are limited to the SQL schema that SharePoint uses behind the scenes. I should remember what the limits are but it's been 7 years since my dev team at Microsoft designed them... Anyway, my guess is that for text controls, SharePoint limits the column width to 255 chars but that it's bigger for rich text. I know that wasn't what you wanted to hear.
Several ways to work around this:
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Add a rich text control to your schema and change the text control in your schema to bind to that instead. Then, promote that to SharePoint instead of the current one.
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Save your data to a SQL database and use data views
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Pros: data views unleash a lot of flexibility. You can customize them using SharePoint Designer.
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Cons: you need to get your data in a real database (not SharePoint). Qdabra provides a free trial of a Web Service that will do this very quickly and no changes to your form are needed.
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Map your data to a SharePoint list instead of Form Library and use Qdabra's client-side qRules to promote XML values to it on Submit
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Pros: no SQL or Web Service required,
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Cons: ShP lists may have their own limitations and you need to check those first by just creating a list and typing in a long text string. If they work, you will still need to inject qRules into your form and set up the mapping. qRules is $199 and it will take an hour to configure the mapping.
There may be another solution, but these are the three workarounds I can think of for now.
Good luck!