The phrase "a substantial overall reduction" is correct and usable in written English.
It can be used when discussing a significant decrease in quantity, size, or degree in various contexts, such as finance, environmental impact, or resource consumption.
Example: "The new policy aims to achieve a substantial overall reduction in carbon emissions over the next decade."
Alternatives: "a significant total decrease" or "a considerable overall decline."
Participants entering work showed a substantial decrease in mental health service costs which outweighed a slight increase that was observed in non-psychiatric secondary care, leading to a statistically significant overall reduction in health and social care costs.
On average, patients in the metformin arm had a substantial average overall reduction in incidence of diabetes, but this benefit was almost entirely a result of those at the highest risk experiencing a dramatic relative risk reduction (as measured by the hazard ratio) and absolute risk reduction (table 3; fig 2).
Despite substantial cuts to police budgets there has been a 6% overall reduction in crime in the year ending June 2012.
The proposed DAC structure allows a substantial reduction in overall control logic complexity.
Heat transfer results indicate a substantial reduction in overall temperature with effective concentration of thermal power density in the designed material.
But Arpey told AP that, over the same period, his managers had seen "a substantial reduction in overall compensation" because stock-based payouts were low.
The eyes laid much deeper in the head than seen normally and, when the overlaying eyelid tissue was removed, a substantial reduction in overall eye size became apparent in homozygous Dicerfl/fl; cre+ embryos (Figure 3).
Because eIF2 is more abundant than eIF2B, a small amount of eIF2α-P is sufficient to sequester a large proportion of available eIF2B, leading to a substantial reduction in overall protein synthesis.
We will be making a 15% overall reduction in headcount across the company.
However, following either of those courses of action leads to a substantial reduction in the overall image brightness, significantly reducing the impact of the HDR effect and reintroducing - albeit to a much more limited extent - some of the light balancing issues noticed on 2016's models.
