What is the scope of the obstruction-of-justice enhancement in criminal law?

Section 3C1.1 of the Guidelines instructs the district court to increase the defendant's offense level by two levels if "(1) the defendant willfully obstructed or impeded, or attempted to obstruct or impede, the administration of justice with respect to the investigation, prosecution, or sentencing of the instant offense of conviction, and (2) the obstructive conduct related to (A) the defendant's offense of conviction and any relevant conduct; or (B) a closely related offense." U.S.S.G. 3C1.1. Thus, the obstruction-of-justice enhancement applies only if the obstructive conduct related either to "the defendant's offense of conviction" or to "a closely related offense." Id.; see also United States v. Byors, 586 F.3d 222, 227 (2d Cir. 2009) (interpreting this provision to create a "nexus element"); cf. United States v. Zagari, 111 F.3d 307, 329 (2d Cir. 1997) (discussing application of obstruction-of-justice enhancement based on perjured testimony given in a "related proceeding").