The more energy the interceptor is forced to dissipate by counter/reaction maneuvering, the smaller its engagement envelope becomes. The area it is able to protect becomes smaller, to a point, at which it will never reach the attacking missiles rendezvous position at all.
In the case of the mach 12 Haj Qasem missile, energy must be dissipated in order to slow it down to below mach 6 at impact. Hence the kinetic energy equivalent of 6 mach numbers is available to its MaRV for late cruise phase and terminal phase maneuvering. The dissipated energy will heat up the MaRV and cause the desired positional changes.
Relatively low g maneuvers that change the heading angle by few degrees will, at those high speeds, create large difference in distance of missile to interceptor. The more energy reserve/speed is available, the more such heading angle change cycles can be performed, to which the interceptor must react, since it doesn't know what the intended target is.
As the maneuvers become more intense the closer the missile comes to its target, it suddenly goes vertical with highest intensity maneuvering to hit the intended object from above. This vertical dive maneuver increases the unpredictability and makes interception more difficult.
The Iskander can only perform late and relatively few maneuvering cycles during its vertical dive, primary intended to defeat PAC-3 and David Sling type terminal ABM interceptors. Haj Qasem starts earlier, with more cycles, of more severe vector variations.
This improves its performance against high kinematic capability, area-defense interceptors like the Arrow-2 and further reduces engagement envelopes to points where the ABM system itself can be attacked.
