My working ratio is closer to six times cost than four. With 0.2 spread, 0.6 commission and 0.2 average slip, I need about 6 pips of average winner before I call the setup scalpable on EURUSD during London.
A 3 pip target failed that test even when the win rate looked fine on a gross log. After costs the expectancy sat near zero across a 250 trade block, so I either stepped to M5 targets or skipped the hour.
Limit entries helped on the entry side but did nothing for stop slip, which is where most of my cost budget went on fast tapes. Widening the stop without widening the target just made the ratio worse.
I also cut pairs whose London open spread alone already eats a third of the planned target. That filter removed GBPJPY from my morning list.
What ratio do you actually require before a pair stays on the card? I recompute it whenever commission tiers change.