Wick Extremes Against Body Extremes
One definition of the boundary is chosen once and then never changed. Wick extremes and body extremes are both defensible ways to mark an opening range, they differ by a meaningful number of ticks on most instruments, and the difference is largest on exactly the mornings when it matters most. The list of measurement conventions, and this is the first entry on orb trading setups beekeeping for beginners because everything downstream depends on it, exists so the choice gets made away from a live chart rather than at the moment one version happens to favour the trade already wanted.
The Case for Wicks
The wick is where price actually traded, and a stop placed beyond it is beyond everything that happened during the period. That is the conservative reading and it produces fewer stop outs on noise. It also produces a wider stop, a smaller position size, and a worse risk reward on any fixed target.
The Case for Bodies
The body extreme is where price was accepted rather than merely touched. A break of it happens earlier, the stop is tighter, and on ranges with long tails the two levels can be a long way apart. The cost is more frequent stop outs on ordinary movement, since the level sits inside the noise band of the period.
Neither is correct in general. What is incorrect is switching between them, because the switch always happens in the direction that makes the current chart look better.
Where the Difference Is Largest
On a range with two long wicks and small bodies, the two definitions can differ by a third of the total width. On a range made of solid directional candles they differ by almost nothing. So the convention is irrelevant most mornings and decisive on the wick heavy ones, which are also the mornings with the widest stops and the most temptation to reinterpret.
Record Both for a Quarter
The cheap way to settle it is to log both numbers for sixty sessions while trading only one of them. That gives a direct comparison of how often the tighter level would have been stopped out and how much earlier it would have entered. Sixty sessions on one instrument is enough for a difference to show if there is one.
Whichever Is Chosen, Write It Down
The convention belongs in the written rules alongside the range length, because a rule saying break of the opening range is not a rule until this is specified. Two traders following the same published strategy with different conventions are running different systems, and a backtest built on one says nothing about live results produced under the other.