If we haven’t imported energy in the first half of the SP, then we could exceed the power constraint in the second half, as long as the total energy in the half-hour does not exceed the (constraint * 0.5hours) kWh. This is because the constraint is monitored and billed as the energy within a half-hour.
This might improve our performance as we have a small import constraint at some sites, and only get the imbalance price signal late into the SP. But we'd need to make sure this is allowed.