It comes down to the ratio of pitching to rolling inertias B/A. The yawing inertia is the largest – approximately being defined by C~B+A, and so its actual value tends not be significant in determining the spinning characteristics. The two smaller rotational inertia values, B and A, and specifically their ratio, tends to define the spin mode and the response to roll (aileron) input during the spin.
When B/A<1, the aircraft is often referred to as “wing dominated” which tends to imply a spin-prone aircraft. When B/A>1, the aircraft can be referred to as “fuselage dominated” or “pitch dominated”, which tends to imply spin-resistance. So, biplanes or aircraft with wing-mounted engines will tend to be more spin-prone than monoplanes or aircraft with fuselage mounted engines; although this is a trend and not an absolute rule.
Ailerons act in the normal sense during the spin. So, if the aircraft is wing-dominant, in-spin aileron will tend to cause the roll to couple with yaw, increasing the spin rate (the Scottish Aviation Bulldog is well known for this, but far from alone), also tending to flatten the spin. The converse will also be true, so:
Fuselage dominant aircraft
in-spin aileron tends to reduce spin rate
out-spin aileron increases spin rate and flattens the spin.
Wing dominant aircraft
in-spin aileron tends to increase spin rate and flatten spin.
out-spin aileron tends to reduce spin rate.
Of-course, this is all gross generalisation, and I'm sure with a bit of effort you'll not have too much trouble finding aircraft tht contradict me, but it's a reasonable general rule.
G