@comboardq not exactly sure what you are asking, however, the instructions for form 6198 would be a good source.
File Form 6198 if during the tax year you, a partnership in which you were a partner, or an S corporation in which you were a shareholder had any amounts not at risk.
Form 6198 deals with at-risk, which essentially is the same as basis for an S corp; if you don't have basis, you aren't at-risk.
The IRS also introduced a new form 7203 to have some consistency in maintaining basis. In the past, S shareholder's would be required to attach some form of support for losses, but no specific format existed.
I can't tell you the interplay of these two forms within TT, but my guess, is form 6198 will be needed for any limitation of losses within TT.
In reading your linked post, form 6198 is not an entity level form. This is prepared at the shareholder level.
*A reminder that posts in a forum such as this do not constitute tax advice.
Also keep in mind the date of replies, as tax law changes.
