[Screenshot comparison with Central-Anime - 1080p](https://slowpics.org/comparison/881c0e62-7366-4df2-958a-9cfdf934db32)
[Screenshot comparison with DmonHiro - 720p](https://slowpics.org/comparison/f0d7f62a-1a39-466b-9bb0-d8ee140a711d)
Encoding is not an important part of the fansubbing process anyway xD
The big size is due to all the dark scenes, which in addition also have a hell of a lot ships moving (with it's effects: e.g. attack afx) all at once, and the master res is also pretty high. And due to that it is necessary to have good filter and encode settings.
The size saved with a HEVC test encode wasn't sufficient enough to preserve the same amount of details as in 264.
If you actually care and want a good quality encode for this show, a big size is more or less a need. Except you want 400MB per eps and can't even tell a planet apart from a crushed potatoe.