H.265 worse than H.264?

[guju]

This may seem no genuine question for Avidemux,
but as it may have to do with the parameter Avidemux uses
I do place it here anyway.

To save place on my hd I usually transcode mpg2 movies to H.264.
Using parameters tuning = grain and crf18
produces the quality I do want.
Typically this takes about 20 mins, using 8 cores @ 100%.
The resulting file size varies from 40% to 90%.

Recently I tried H.265, expecting it to produce better results.
From the default values I just changed tuning to "grain" and
compression to crf18.

The result:
The transcoding took about double as long
(which might be expected and therefore acceptable),
using the 8 cores to only 80%.
The resulting filesize was about 10% larger than the H.264,
and the visual quality was worse than H.264 (less detailed).

Do I did something wrong?

[Elstar`]

Just use H.264, there are no real improvements of quality in H.265, only compression (with tradein for quality).

You can also further improve H.264 quality by disabling Macroblock tree (in Advanced RC) and set both psy_rd tunings to 0,00 (Psychovisial Rate and Trellis in Analysis).

[Fergar]

You can also further improve H.264 quality by disabling Macroblock tree (in Advanced RC) and set both psy_rd tunings to 0,00 (Psychovisial Rate and Trellis in Analysis).

Could you explain why those settings are better?

[Elstar`]

You can also further improve H.264 quality by disabling Macroblock tree (in Advanced RC) and set both psy_rd tunings to 0,00 (Psychovisial Rate and Trellis in Analysis).

Could you explain why those settings are better?

It results in much less blur (and slightly higher bitrate).