J.J.S.

Such explanation is also included in Dynamit Nobel Defence marketing brochure: For the same reason they developed CLARA ERA with composite plates instead of metal ones. However, almost all weapons with SC that have been designed for last 30 years still have warheads with precursor. Modern ERA have improved reaction time, good example of this is russian 4S24 in comparison with 4S20. Moreover, thick passive plates placed in front of reactive armor can significantly erode jet tip and reduce its velocity. For example there is 50 mm of steel between ChSKW-34 layers in Duplet from Oplot-M hull and 25 mm in front of 4S22 in T-72B ob.1989. Even 10 mm thick steel plate has noticeable effect.

I have no idea where you learned physics to conclude that steel cuboid with 150x150x6 mm dimensions has the same or higher weight than steel cuboid with 150x150x10 mm dimensions, excluding the additional mass of cassete sides, screws and mounting beam. Then learn Gurney equations.

The shape of liner is not all. To reduce energy of of jet/slug it is possible to either decrease its velocity or density. I think that you forgot what Vasiliy Fofanov wrote about PG-7VR: Fragment of article from russian miliary journal Kalashnikov: Explosive used in 4S23 has improved sensitivity in comparison with 4S22. It might explain why Relikt is claimed to be very effective against tandem RPGs.

The purpose of using EFP precursor in this case is NOT to initiate ERA, 4S20 and 4S22 won't detonate on EFP (and other low velocity projectiles) impact. Tandem RPGs like Panzerfaust 3-T, PG-7VR (russian ATGMs don't) use non-initiating precursors to increase the safety of infantryman using them against tanks with ERA at short ranges. On the other hand, such precursors are almost useless against targets with good passive protection against HEAT. On the picture below it is shown what they do with Kontakt-5. This lower part is quite heavy and will move with lower velocity than upper plates. Moreover these mounting beams will additionally slow it down. That's why such movement shouldn't be efficient against cumulative jet.

The main difference between 3-T and and final 3-IT600 that might explain such results, is precursor warhead shape. During other tests EFP precursor with 40 mm diameter proved almost totally ineffective against ERAWA-2 (no perforation of upper plate). I think that it's impossible to fully reduce reactive armour efficiency by simply increasing jet tip velocity (with copper liners it's also difficult to exceed 10 km/s) taking into consideration this fragment of "Evolution of ERA for light-armoured fighting vehicles" :