Most have their zero around 25... because their mounts are common... and the other reason is you may only see a click 5yds either side of 25, perhaps two... so it can be missed or ignored as a significant change if you are so inclined.
I tend to set up the ranges loosely to work out where the lowest point is, then lift and shift the turret to zero at that point, but perhaps set it to 4-5 clicks, just to allow a little room for error or shift.
If you're obsessed like me though, you can make a graph and see where your actual zero is by plotting clicks vs distance... sometimes it isn't bang on 25 yds... if you look at the attached image, you can see that the actual top point of the trajectory is about 32.5 yds... This is H's rifle, which has a scope centre to bore centre of about 100mm or so...
it can be a useful exercise to see if you have any odd humps n bumps... when i do it i just try and smooth the curve out a bit, but there's normally a couple of ranges that seem to be a click or so out off the line... i dont let it bother me in that case. Can be a saving in time by doing a guestimate of your clicks at 'in between' ranges like 2.5 yds apart.
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