I had 2 IS2s cause for about 50-60% of the game I had 2 fuels or he was cutted from his fuel. That's why it was 2 IS2s vs 1 KT. Usually it's 2 IS2s vs Jadgpanzer+KT or Panther+KT or 2 Panthers.
But like I said many times. 375 is to big nerf for KT. If the wanted to nerf it, 400 would be perfect.
You didn't need to have him cut off or anything to have 2 IS2s by the time he gets a KT.
KT= 40+80+260=380 / 0.66= 575
Even if you both get equal territory, by the time he gets enough resource to get a KT you get 575 fuel.
IS2=230, 575/230= 2.5
That is 2.5 IS2s by the time you he gets fuel for KT, in case you both get the same territory.
Now let's take a look at the other cases you mentioned:
JP+KT= 380+135= 515 / 0.66= 780.3, 780.3/230= 3.39 : That's 3.4 IS2s vs KT+JP
Panther+KT= 380+175= 555 / 0.66= 840.9/230= 3.66 : That's 3.7 IS2s vs KT+Panther
2 Panthers= 80+175+175= 430 / 0.66= 651.52/230= 2.82 : That's 2.8 IS2s vs 2 Panthers