Re-create the patchwork quilt. Whatever the agronomic benefits, for wildlife, one of the worst aspects of modern agriculture is farming in blocks. Set-aside all in one chunk, and the rest of the farm divided into two blocks of either oilseed rape or wheat is not good for game or other wildlife.
Animals like to have a variety of habitats within easy reach and block farming prevents this. A hare likes about eight different fields in the course of the year; young wheat in winter, spring barley in April, grass ley and pastures in the summer, oilseed rape in the autumn - along with catch crops like turnip and mustard.
Old fashioned rotations produced a patchwork quilt which is ideal. If you can’t abandon the big block system then try at least to use some of the ELS options and set-aside to create more of a patchwork. Some ideas are:
Retain some over-winter stubbles (EF6). Cereal stubbles are best and, if you hand sow in some patches of mustard, it will provide good game cover as well.