Pacing & saturation diagnostic
Average cost after a budget change almost always looks fine. This checks the marginal cost instead, what the last increment of spend actually bought, compared to two periods of your own numbers.
Prior 2 weeks
Most recent 2 weeks
Marginal cost vs average cost
1.93x
Saturating
The last pound of spend is buying meaningfully more expensive conversions than your average suggests. More budget at this pace won't scale efficiently, the constraint is the audience/inventory, not the budget.