Kontakt-5 was first deployed on T-80U models around 1985 so it is period-appropriate. The general consensus on tanknet.net, while it was around, that it adds roughly ~250mm of armour vs. KE penetrators, largely due to the angle of incidence (AOI) of these types of rounds vs. the lower AOI you'd get from an arcing HEAT shell or top-attack missile (so that their effect would be much greater). This results in 650mm+ vs. KE and over 1000mm vs. HEAT, with a limited bonus vs. two-stage or 3-stage HEAT penetrators.
In the game Fistful of Tows, various generations of T-series tanks have armour modelled as such:
T-55A 8 A 7
T-72 10 A 7
T-72B 12 A 9
T-80 10 A 7
T-80B 11 A 9
T-80U 13 C 10
The first number is the arnour rating vs. KE (including ERA effect, if any), the letter is the HEAT rating (including ERA) and the last number is the flank armour.
For reference, a Leopard 105mm L7 gun has a penetration of 11/11h (KE/HEAT or HESH)
A TOW-2A has a 19h2 penetration, meaning it's a 2 stage warhead and the C armour code (composite armour + ERA) of the T-80U offers better protection than the A armour code (just composite armour) of the T-80.
I think T2000 v4 lacks sufficient fidelity in armour ratings to try to model Kontakt or other ERA accurately. I guess you could just add a +1 or +2 to ARMOR and call it even because the type of HEAT or KE penetrator is not being modelled either (e.g. world's of difference between a TOW and a TOW-2A).