Price stopping a few pips short of an obvious level

[FXS Prop Desk]

My bigger worry is that you'd need a fair few sessions of data before the baseline means anything

Fair objection on the workload. It doesn't need a spreadsheet though: a plain 20-bar average drawn on the tick volume pane gets most of the benefit, even if it isn't matched by hour. You're probably right that for turns inside the London open the busy-versus-busy comparison barely changes anything. Where it tends to earn its keep is the odd level test at 10:30 or after lunch, when a bar looks normal on the chart but is thin for that time of day. If nearly all your turns were at the open, skipping the filter is a reasonable call.