I used to work on a fairly big partridge shoot down south before i moved on the grouse.
We used a mixture of millet, dwarf sorghum and linseed in our cover crops, the linseed and millet provided little cover but lots of food/seeds and the sorghum was the opposite, so together they worked well! The reason we used three different things in the mix is because we could put this down as 'wild bird cover' on certain schemes (the entry level scheme i think) and had it either paid for or got a good lot of money put towards it! Depending on who owns the land/has the farming on it, i would definately