Wrong bitrate when converting from 88200Hz

[Rainoutt]

When converting from 88200Hz sample rate, it switches the bitrate (instead of using 128 it uses 160)

00 - Here Without You.m4a
88200Hz -> 48000Hz
AAC-LC Encoder, ABR 160kbps, Quality 96
[100.0%] 3:59.613/3:59.613 (10.7x), ETA 0:00.000
11501440/11501440 samples processed in 0:22.359
Overall bitrate: 159.91kbps
Optimizing...done
qaac 2.80, CoreAudioToolbox 7.10.9.0
00022.` Hells Bells.m4a
96000Hz -> 48000Hz
AAC-LC Encoder, ABR 128kbps, Quality 96
[100.0%] 5:12.815/5:12.815 (25.7x), ETA 0:00.000
15015134/15015134 samples processed in 0:12.188
Overall bitrate: 127.551kbps
Optimizing...done
qaac 2.80, CoreAudioToolbox 7.10.9.0

Is this intended behavior? Here is the command :
for %%i in (*.flac) do qaac64.exe "%%i" -a 128 -q 2 --copy-artwork

[nu774]

160kbps is the lowest for 48kHz/5.1ch (which you can see by qaac --formats).
Isn't that file 5.1ch?