Due to pine limitations, bin size and the sample lower time frame selection will have at least some effect on the accuracy of the approximation. The trade off is between accuracy and historical availability, however bar replay can be used to view prior historical states beyond what is visible from the current real time bar.
In order for all intrabar POC circles to be visible, you will need to manually set the visual order of the indicator by bringing it to the front.
Since the POC represents a price point around which the highest market participation occurred, the exposed global variable intrabar_poc may (or may not) be interesting as an alternative to ohlc based source input.
In true TradingView spirit, the author of this script has published it open-source, so traders can understand and verify it. Cheers to the author! You may use it for free, but reuse of this code in a publication is governed by House Rules. You can favorite it to use it on a chart.