The same modest improvement was observed when splitting the grammar with segment length 4, where we moved from 45.0 cross-entropy to 44.5 (model fstg_c_c to fstg_c_c_s2).
splitting again gave 42.9 (moving to fstg_c_c_s2_s2), and a third time gave 39.5 (moving to fstg_c_c_s2_s2_s2).