how to optimize parallel bulk inserts waiting on IMPPROV_IOWAIT

is there a way to optimize a parallel bulk insert that's waiting on IMPPROV_IOWAIT? (get rid of the waits)

so far tempdb has >= number of files than then number of parallel loads and so is the destination database and  table is partitioned.

we are using the SSIS bulkload operator the destination table haswith no indexes (a heap)

there are 45 different parallel loads - file size is  205 MB we have a 48 core machine on 250 G of RAM and currently the load takes 3minuted 17 seconds which I think might be optimized better

this post is somewhat related to (see below) that is now resolved

 https://social.technet.microsoft.com/Forums/en-US/54cdbf4b-3471-4e27-9fc8-a12dba2e249c/bulk-insert-parallel-load-causing-blocks?forum=sqlintegrationservices

eddy.a