I would zero it the same way you intend to use it. If you're going to shoot it from a bag then zero it from a bag, if you're going to shoot it one-handed ISSF style then zero it that way.
I took my new (to me) Browning HiPower to the range this arvo. I just wanted to ensure it runs so I put 90rds through it very quickly, two-handed (we were starting a Rapid Fire match in twenty minutes and we still had to set up the targets). Everything worked fine, slide locked back on all five mags, mags dropped free nicely. I wasn't at all concerned about putting rounds on paper as this is factory ammo. I'll work up my own load with cast bullets, and then I'll work on accuracy and zeroing. But the interesting thing is that shooting very fast (five mags in probably ninety seconds max, then reload all the mags) the rough centre is perhaps four-inches low at 25m.

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But when we finished the Rapid Fire match, two of my mates each put a mag through one-handed ISSF style (but they held at 6 o'clock so they were all just below the bottom of the target page), then I put a mag through ISSF style, but holding on target centre, and my shots also grouped below the bottom edge. So I want to play with that next time to see if the different shooting stance really does affect point of impact that much.
90 rounds fired on the target, and I count about 60 single holes and the big chunk that is shot away, so they were in the ballpark, I'm sure I threw away a lot of the double-taps. On the weekend I hope to do some shooting resting on the bench to get an idea of the accuracy of this ammo in the pistol. But for now I know this ammo runs the gun fine. So I'll chronograph it in the 7" 9mm Chiappa 12ga. barrel, then work up loads that match that velocity, and they should run fine in the gun as well. From there I can tweak it for best accuracy, and then I can look at zeroing the pistol with that load to point of aim at 25m, from a modified Weaver stance.