The IS-2 has 140 rear armor;
The KV-2 has 120 rear armor;
The Pershing has 110 rear armor;
The Churchills all have 180 rear armor.
The Tiger I has 140 rear armor;
The Tiger II has 150 rear armor.
The KV2 has 180 rear armour too, not sure why you wrote 120. Was it nerfed recently?
You also forgot the KV1 at 165 which is also pretty high and KV8 at 145.
Also that makes the AVRE, regular Churchill and Crocodile all have 180 rear armor.
Seems a bit too much IMO. 155 rear armour on the ISU isn't really needed either considering you will have to flank it unless you have Elefant on the field. I don't really think a flanking P4 should bounce point blank shots against the rear armour of an ISU when the whole point of the unit is to flank it in order to get it killed.