most of wedge shape modular armour seen type-99 and type-96 B appear to be 60 degree slope,which is insufficient to stop long rod penetrator like M-829.
according to mathematic calculation make by P. lakowski, wedge shape armour plating needed 70 degree to repel the penetration.if you look at wedge shape armour in leo-2 and merkava tank most modular armour slope at 70 degree.
60 degree slope armour found in type-99 and type-96b more likely design for ERA attachment.
70 degrees is not what is required to stop a sabot, it is what is required to deflect it so that the round ricochets off of the armour instead of being stopped by it.
The 70 degrees was also calculated based on standard steel armour instead of ERA. Normal ERA works either by using the explosive force to shatter the penetrator or via a 'guillotine' principle whereby the explosives forces two metal plates to move rapidly enough to cut the tip off of a penetrator, thereby massively reducing it's armour piercing capabilities.
I can see no fundamental technical difficulty in designing ERA specifically designed work with sloped armour so that instead of cutting the tip or trying to shatter the penetrator, the explosive force of the ERA is channeled so that it forces the penetrator to angle away from the armour such that when it connects with the sloped armour below the ERA, its angle of incident is greater than 70 degrees.
Now I am merely suggesting that such ERA is perfectly feasible, but whether anyone has bothered to develop it is another matter. But regardless, the point is that a) you do not need a 70 degree slope to stop a penetrator, and b) it is possible to achieve the required angling to defect a penetrator with specially developed ERA even if the hull is below 70 degrees of slope.
