I have found that for OTM options, the decay occurs in a more linear manner with a bit of acceleration towards the end (final 2-3 weeks). This acceleration is much more pronounced the closer you are to ATM, but I would say max acceleration occurs in the last few days (or hours) not in the 40-20 DTE period.
I didn't mean to say that 40-20 dte is peak acceleration, but simply that it is the time frame when the decay becomes more noticeable. Sure the decay in the last few days is greater, but it's a way more dangerous spot to be short..