I used X-plane 10 and 9 for my real life instrument rating training .
Not sure what you mean by too small . The instruments are/were perfectly visible . They are/were accurate allowing for sometimes less than completely accurate flight physics.
I sometimes would find shooting an ILS in otherwise CAVOK conditions ,the needles rate of change a little too fast compared to a real aeroplane .
If you mean by cockpit the whole physical replica of a cockpit then x-plane is used for this purpose too.
If you just want a system that is dedicated only to IFR training then flyelite may be what you are after. The eye candy in flyelite is spare as far as outside visuals are concerned but the panel representations on screen are excellent.