The presumption does not create a Sixth Amendment violation because it does not require the sentencing judge to impose a sentence within the Guidelines range, even if it will ultimately have the effect of encouraging judges to impose within-Guidelines sentences more frequently. Somewhat counterintuively, because the Sixth Amendment violation occurs when a judge imposes a sentence higher than she would otherwise be able to based on "jury-determined facts standing alone," there is no Sixth Amendmdent violation because a presumption of reasonableness does not require a judge to impose a sentence above whatever would be the Guidelines range based solely on the jury's findings.