bbref says he played 33% or the time at PF and 68% at C
82games says the breakdown was Sabonis played 11% of Indy's PF minutes and 35% of their C minutes.
so, they seem to have the breakdowns about the same. 82games breaks it down a little more: Sabonis was a slightly better offensively at C, going by PER and rebound rate; better eFG% at PF though. But Sabonis was much better defensively at PF. He gave up a PER of 22.4 at C and 13.5 at PF
going by the numbers at 82games, Sabonis was a better overall PF last season than Zach. He just didn't play as big of chunk of his minutes there:
http://www.82games.com/1819/18IND16.HTM
http://www.82games.com/1819/18POR15.HTM