Interesting, TIL the tables I've played at may have been interpreting these kinds of spells wrong.
Do you happen to have an official comment disambiguating this? If not that's fine. Basically the reasoning has been "when you cast it is also the first time they enter the spell area", although it did seem like a lot of damage for that level of spell.
I have a P7P. I really like it, my only issue is the SoC being a little slow! But for most usage you don't really notice.