Thanks for your engagement with the report and this question! Our next report is now out, which addresses this to some extent. We found that mortality does decrease as farm intensity increases, but the data here is limited. I also did a quick BOTEC (numbers are rounded):

This is very rough and mortality rate is going to vary hugely between farms and over time, but it suggests that your suspicion is correct—it looks like extensive farms could be responsible for the highest fraction of shrimp deaths, followed by intensive farms.

Details on data in the BOTEC:

• Our first report found that 440 billion shrimp are slaughtered annually. 
• Proportion of production is reported by Boyd et al. (2022, p.33), who estimate that in 2018 it was 11.5% Extensive, 16.7% Semi-intensive, and 71.8% Intensive. They don’t report super-intensive, so we assume at the time it was <1%. But, because this source is ~6 years old and the industry has likely intensified since then, we put it at 1%, and reduce the other three farm types by 0.333…%.
• Mortality rates from our new pre-slaughter mortality report (see Figure 6), I took the mean of the means reported for each farm type.