Initial extent size when converting to partitioned table

Working in an Oracle 19c database on Linux x86/64 trying to convert non-partitioned table to partitioned table.

Since Oracle12, alter table modify partition has been available to convert non-partitioned tables to partitioned tables. I have a non-partitioned table that has the initial_extent size set to 544MB. This is way too large. The actual first extent is 8MB.

When I use the alter table modify partition, I end up with 90 partitions all with an initial extent of 544MB. this results in the tripling of the size of the table. Many partitions are 90% plus empty.

Question is this. How to set initial partition extent size to a reasonable value during this process?