The diagnostic bar standard uses a 50% open which means it fills in on the 1st tick of the formation of that bar from the open to the 1st tick with the open plotting at 50% between the open and the close of the previous bar. It used 100% of the brick/tick size for reversal size. For a 12 tick bar size it would mean 12 ticks from the painted open (that is 50% between the open and close of the previous bar) so if the market moved up to a price that was 12 ticks above that open and moved 1 more tick up or down to a price that is 12 ticks below that open and moved 1 more tick down it would close the bar and plot the 1st tick of the new bar. This allowed for diagnostic bars to paint accurate highs, lows and closes and smooth out the chart with the 50% open. Since indicators are based on the close this had no impact on indicator calculations.
We also have Shadow Bars and Continuum Bars, be sure to the see the Forum section for both of those as well