Exchange Fragmentation Means Your Level May Differ
Draw an opening range on a chart and it looks like a fact about the instrument. It is not. It is a fact about the venue the chart is sourcing from. Another exchange, watching the same asset over the same minutes, produced its own high and its own low, and those numbers are close but not identical. A strategy whose entire trigger is price crossing a specific level has a problem hiding in that gap.
Why the Prices Differ at All
Each venue is a separate order book with its own participants, its own depth and its own flow. Arbitrage keeps them close, because a meaningful spread between two books invites someone to close it, but that process takes time and capital and it works best when conditions are calm.
The corollary is uncomfortable. The discrepancy is smallest when nothing is happening and largest during fast moves, which is precisely when a break of a level is being decided. The moment you most need the price to be a single agreed number is the moment it is least likely to be one.
What This Does to the Trigger
Suppose your range high came from one venue and the break happens on another. Your chart may show the level cleared while the book you actually trade on has not reached it, or the reverse. The trade either triggers on a level that was never crossed where it matters, or fails to trigger on a level that was.
Neither is catastrophic on its own, and much of the time the difference is inside the noise. What it does over a long run is add a layer of variance that has nothing to do with the strategy and cannot be improved by refining the strategy. It shows up as slightly worse fills, occasional entries that make no sense in retrospect, and a scattering of missed setups that looked valid on the chart.
Aggregated Prices Are Not a Clean Fix
The obvious answer is an index or aggregated feed that blends several venues, and it does produce a smoother, more representative number. It also introduces its own issue: you cannot trade the index. Your order goes to one book, and the level you drew is now a synthetic price that no book is obliged to reach.
An aggregate is better for judging whether the asset broke out. A single venue is better for judging whether your order will fill. These are different questions and it is worth being clear about which one your level is answering, because a chart cannot tell you.
Match the Chart to the Book
The most reliable arrangement is the least clever one. Draw the range on data from the venue you execute on, so the level and the fill live in the same place. It gives up a little representativeness in exchange for removing an entire category of unexplained result, and unexplained results are what make a record impossible to learn from.
If you trade across more than one venue, then more than one range exists and there is no way around that. The practical answer is to treat each venue as its own instrument with its own levels rather than pretending a single line governs all of them.
Where It Actually Bites
This matters most for thinly traded assets, where the gap between venues is wider and persists longer, and least for the largest and most liquid, where arbitrage closes discrepancies quickly enough that the difference is rarely decisive. It also matters more the tighter your trigger is. A rule requiring price to clear the level by a visible margin is largely insulated from a small discrepancy, while a rule triggering on the first tick past it is exposed to all of it.
That suggests a specific and cheap adjustment. A break buffer wide enough to swallow the normal spread between venues costs a small amount of entry price and removes most of the exposure. It is not elegant, but the alternative is a trigger whose behaviour depends on which data provider you happened to open that morning.