No, I don’t think, that you have overseen something. I haven’t seen an explanation why there has been left just half of the size for the running system. Anyway I accepted that, because together with my SD-Card for me it’s enough space.
My guess is, that some stuff is needed for recovery system and android blobs. if you look at the partition layout, you see, that all the space is there but used for different things:
[root@Phone22 home]# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINTS
loop0 7:0 0 448,4M 1 loop /android/apex/com.android.art
/android/apex/com.android.runtime
/android
/android/system
/var/lib/lxc/android/rootfs
loop1 7:8 0 392,9M 1 loop /android/vendor
loop2 7:16 0 58,6G 0 loop
└─home_encrypted 253:1 0 58,6G 0 crypt /home
nbd0 43:0 0 0B 0 disk
nbd1 43:32 0 0B 0 disk
nbd2 43:64 0 0B 0 disk
nbd3 43:96 0 0B 0 disk
nbd4 43:128 0 0B 0 disk
nbd5 43:160 0 0B 0 disk
nbd6 43:192 0 0B 0 disk
nbd7 43:224 0 0B 0 disk
mmcblk0 179:0 0 116,5G 0 disk
├─mmcblk0p1 179:1 0 3M 0 part
├─mmcblk0p2 179:2 0 512K 0 part
├─mmcblk0p3 179:3 0 512K 0 part
├─mmcblk0p4 179:4 0 20M 0 part
├─mmcblk0p5 179:5 0 1M 0 part
├─mmcblk0p6 179:6 0 8M 0 part
├─mmcblk0p7 179:7 0 8M 0 part
├─mmcblk0p8 179:8 0 8M 0 part
├─mmcblk0p9 179:9 0 8M 0 part
├─mmcblk0p10 179:10 0 8M 0 part
├─mmcblk0p11 179:11 0 8M 0 part
├─mmcblk0p12 179:12 0 22,6M 0 part /metadata
├─mmcblk0p13 179:13 0 32M 0 part
├─mmcblk0p14 179:14 0 32M 0 part /mnt/vendor/nvcfg
├─mmcblk0p15 179:15 0 64M 0 part /mnt/vendor/nvdata
├─mmcblk0p16 179:16 0 48M 0 part /mnt/vendor/persist
├─mmcblk0p17 179:17 0 8M 0 part /mnt/vendor/protect_f
├─mmcblk0p18 179:18 0 8,4M 0 part /mnt/vendor/protect_s
├─mmcblk0p19 179:19 0 8M 1 part
├─mmcblk0p20 179:20 0 128M 1 part
├─mmcblk0p21 179:21 0 1M 1 part
├─mmcblk0p22 179:22 0 6M 1 part
├─mmcblk0p23 179:23 0 1M 1 part
├─mmcblk0p24 179:24 0 16M 1 part
├─mmcblk0p25 179:25 0 2M 1 part
├─mmcblk0p26 179:26 0 32M 1 part
├─mmcblk0p27 179:27 0 64M 1 part
├─mmcblk0p28 179:28 0 8M 1 part
├─mmcblk0p29 179:29 0 6M 1 part
├─mmcblk0p30 179:30 0 2M 1 part
├─mmcblk0p31 179:31 0 26M 1 part
├─mmcblk0p32 259:0 0 64M 1 part
├─mmcblk0p33 259:1 0 12M 1 part
├─mmcblk0p34 259:2 0 128M 0 part
├─mmcblk0p35 259:3 0 1M 0 part
├─mmcblk0p36 259:4 0 6M 0 part
├─mmcblk0p37 259:5 0 1M 0 part
├─mmcblk0p38 259:6 0 16M 0 part
├─mmcblk0p39 259:7 0 2M 0 part
├─mmcblk0p40 259:8 0 32M 0 part
├─mmcblk0p41 259:9 0 64M 0 part
├─mmcblk0p42 259:10 0 8M 0 part
├─mmcblk0p43 259:11 0 6M 0 part
├─mmcblk0p44 259:12 0 8G 0 part
│ └─system_a 253:0 0 7,8G 0 dm /android/vendor/bin/vndservicemanager
│ /android/vendor/etc/init/mtkrild.rc
│ /android/vendor/etc/vintf/manifest/manifest.xml
│ /
├─mmcblk0p45 259:13 0 107,5G 0 part /android/cache
│ /android/data
│ /userdata
├─mmcblk0p46 259:14 0 43M 0 part
└─mmcblk0p47 259:15 0 16M 0 part
mmcblk0boot0 179:32 0 4M 1 disk
mmcblk0boot1 179:64 0 4M 1 disk
mmcblk0rpmb 179:96 0 16M 0 disk
mmcblk1 179:128 0 119,1G 0 disk
└─mmcblk1p1 179:129 0 119,1G 0 part /run/media/defaultuser/86f16387-82ae-48ab-9b14-c834d4c286e8
zram0 254:0 0 3G 0 disk [SWAP]
nbd8 43:256 0 0B 0 disk
nbd9 43:288 0 0B 0 disk
nbd10 43:320 0 0B 0 disk
nbd11 43:352 0 0B 0 disk
nbd12 43:384 0 0B 0 disk
nbd13 43:416 0 0B 0 disk
nbd14 43:448 0 0B 0 disk
nbd15 43:480 0 0B 0 disk
If you are looking at mmcblk0p44 and mmcblk0p45 These should be the relevant partitions. So there is all together 128GB (119 GiB) space. 8GB mmcblk0p44 is for root partition. The rest mmcblk0p44 is for
- /android/cache
- /android/data
- /userdata
In /userdata there is the container for the encrypted home partition (home.img).
Why it has just the given size, I don’t know. Maybe it has to do with the encryption, so there is always enough cache. In the end you have to ask @piggz or someone who is fitter with all this stuff. I’m just a user.