I see the same “pattern” on my system. With 355 Watt modules driving 250 Watt inverters, the result
looks like this: (3 Sept 2020)
In addition to the widened “peak,” performance on cloudy days has improved significantly.
A “mixture” of 235 and 240 Watt modules driving 215 Watt inverters yielded this harvest on 3 Sep 2019:
Same total number of modules in both instances. (44)
https://enphase.com/sites/default/files/Enphase_White_Paper_Module_Rightsizing.pdf
https://enphase.com/en-us/stories/“over-sizing”-v-“right-sizing”-new-ideas-one-solar’s-oldest-debates