Playing 2. e3 suggests a lack of ambition, so rightly or wrongly I raise the aggression level and fight immediately for the centre

Releasing the tension straight away. White should prefer c4 and Nc3.

The knight will be active on c5, and we're forcing White out of familiar positions.

h3 and a3 feel like solutions looking for a problem...

...d5 was possible too, but then Nf3 would delay ...e5

...Ne6 was a good alternative.

White continues developing, but has a cramped position.

Black completes his development. Perhaps his 12th move idea was already possible here?

White should consider o-o.

With ideas of capturing on c2 after moving the e4 knight.