[ by Howard Haykin ] Jamie Dimon, JPMorgan Chase Chairman and CEO, was adamant when he told lawmakers Tuesday his bank was upfront with investors about its multibillion-dollar trading loss, even as regulators investigate whether JPMorgan disguised a dramatic rise in risk-taking.  And with that, Mr. Dimon began his testimony, the second time in a week - he appeared before a Senate subcommittee last week. Yes, he once again acknowledged that JPMorgan in January changed a "value-at-risk" model for the trading portfolio in question.  And yest, the bank did not disclose the change until May 10, when Dimon also revealed that the trading portfolio had produced at least $2 billion in losses. "We disclosed what we knew when we knew it," Dimon told the House Financial Services Committee. Mr. Dimon's comments came after the committee had heard a panel of regulators, including SEC Chairman Mary Schapiro, explain about their agencies' investigations into the trading loss.  Ms. Schapiro said the SEC is looking at whether JPMorgan misled investors in its April earnings statements by failing to disclose the value-at-risk (VaR) change. At that time, Dimon also called press reports about a "London whale" trader with an outsized position a "tempest in a teapot." But whether or not intentional, the model change successfully managed to disguise a spike in the riskiness of the particular trading portfolio by cutting in half its VaR number.  In that context, Ms. Schapiro said, obviously referring to Jamie Dimon:  "If you chose to speak, you absolutely must speak truthfully and completely and not allow yourself to leave any kind of misleading impression from the information that you are putting out." It was at Dimon's testimony Tuesday which followed his appearance last Wednesday before the Senate Banking Committee, where senators were mostly deferential.  A few members of the House Financial Services Committee went harder at Dimon, asking him repeatedly to defend the size of JPMorgan, the nation's largest U.S. bank by assets. Dimon responded: "No, we're not too big to fail," though he added, "I don't think there's any chance we're going to fail." Rep. Sean Duffy (R-WI) asked of Mr. Dimon:  "Is it fair to say JPMorgan could have losses of half a trillion dollars or a trillion dollars?" Dimon replied, "Not unless this Earth is hit by a moon." For further details, go to:  [Reuters, via CNBC, 6/19/12].