Trying to create local partitioned index - taking forever and failing

I  created a 3 million row partitioned table partitioned by list on the project_id. I have created global partitioned indexes and now I'm trying to create a local partitioned index. The global indexes are taking at most 300mb disk space, but the local prefixed index is taking 30gb and still failing with ORA-1659 unable to allocate MINEXTENTS beyond 16.

The table has 4000 partitions.
The SQL is:

CREATE INDEX SYSADM.local_prefix_ix1
on SYSADM.ps_proj_RESOURCE(project_id)
local
nologging tablespace psindex3
storage(initial 50m next 50m maxextents unlimited)
/

The tablespace is locally managed, in autoextend mode with maxextents 32gb.