TOR_SOCKS_IPC_PATH environment variable not honored

I'm building torbrowser from source on gentoo. Reverting two patches to have the profile directory in $HOME

TOR_SKIP_LAUNCH=1 TOR_SKIP_CONTROLPORTTEST=1 TOR_SOCKS_HOST=127.0.0.1 TOR_SOCKS_PORT=9050 /usr/lib64/torbrowser/torbrowser is working as expected.

TOR_SKIP_LAUNCH=1 TOR_SKIP_CONTROLPORTTEST=1 TOR_SOCKS_IPC_PATH=/run/tor/socks /usr/lib64/torbrowser/torbrowser gets me the "Something Went Wrong!" message

Connecting to the socket works after setting network.proxy.socks to file:///run/tor/socks manually in about:config

My /etc/tor/torrc contains:

SocksPort 127.0.0.1:9050 ExtendedErrors IPv6Traffic PreferIPv6 KeepAliveIsolateSOCKSAuth
SocksPort unix:/run/tor/socks GroupWritable ExtendedErrors IPv6Traffic PreferIPv6 KeepAliveIsolateSOCKSAuth