While there are a number of factors that can contribute to turbo lag, such as the size and design of the turbine and compressor, the location of the turbocharger is also a significant factor. In general, rear-mounted turbos tend to have more lag than front-mounted turbos. This is because the distance that the exhaust gases have to travel to reach the turbine is greater, meaning it takes longer for them to build up enough pressure to spin the turbine. Additionally, rear-mounting often results in a less efficient flow of exhaust gases due to bends and turns in the piping.
However, it's important to note that there are many other variables that can affect turbo lag, such as engine displacement, camshaft design, boost pressure, and more. So while rear-mount turbos may tend to have more lag than front-mount turbos on average, there are plenty of exceptions to this rule.