According to the HPE SimpliVity Stretched Cluster Technical Overview1, one of the configuration requirements for implementing a stretched cluster is that the storage network in each physical location must use the same subnet. This ensures that the HPE OmniStack System can communicate with each other across the sites and maintain data synchronization and availability. The other options are not correct because:
The arbiter must be located in a third site that is independent from the two stretched cluster sites1.
The round trip latency must be below 5ms, not 50ms, to avoid performance degradation and data inconsistency1.
A direct-connected network configuration is not required, as long as the network supports jumbo frames and VLAN tagging1. References: 1: HPE SimpliVity Stretched Cluster Technical Overview (51462)

HPE SimpliVity is a hyperconverged infrastructure solution that combines compute, storage, networking, and data services in a single platform. HPE SimpliVity integrates with HPE StoreOnce, a disk-based backup appliance, to provide efficient and reliable data protection and disaster recovery for distributed edge sites12.
HPE SimpliVity uses HPE StoreOnce Catalyst, a deduplication protocol, to replicate data from HPE SimpliVity clusters to HPE StoreOnce appliances. HPE SimpliVity leverages its global deduplication and compression capabilities to send only the unique data blocks to HPE StoreOnce, reducing the bandwidth and storage requirements34.
To optimize the replication performance, HPE SimpliVity uses a dynamic stream allocation algorithm that determines how many streams it needs to copy data to an HPE StoreOnce target. According to the HPE SimpliVity with HPE StoreOnce Reference Architecture document, the algorithm considers the following factors:
The available bandwidth between the source and the target
The latency between the source and the target
The size of the data to be replicated
The number of concurrent replication jobs
The document states that "The available bandwidth is the most important factor in determining the number of streams. The more bandwidth available, the more streams can be used to copy data. However, the number of streams is limited by the latency and the size of the data. If the latency is too high or the data size is too small, adding morestreams will not improve the performance." Therefore, the available bandwidth is the criteria that HPE SimpliVity uses to decide how many streams it needs to copy data to an HPE StoreOnce target.
References:
1: SimpliVity Hyperconverged | HPE 2: Expand backups to secondary storage with HPE SimpliVity hyperconverged infrastructure and HPE StoreOnce 3: HPE SimpliVity with HPE StoreOnce 4: HPE SimpliVity with HPE StoreOnce: A better together story : [HPE SimpliVity with HPE StoreOnce Reference Architecture] : [HPE SimpliVity Data Virtualization Platform] : [HPE SimpliVity Intelligent Workload Optimizer] : [HPE SimpliVity Federation Design and Scaling Guide]

HPE SimpliVity 2600 is a compact solution optimized for edge and remote office, branch office (ROBO) environments. It is available on HPE Apollo 2000 servers, which are designed for high-density computing and can fit up to four nodes in a 2U chassis. HPE SimpliVity 2600 provides enterprise-grade data protection and resiliency for virtualized workloads, as well as simplified management and scalability. It is ideal for customers who have very limited rack space and need a hyperconverged solution that can deliver high performance and efficiency. References: HPE SimpliVity 2600 - Product Information Reference, HPE SimpliVity 2600 | HPE Store US, Introducing Our New High-Density Hyperconverged Solution: HPE SimpliVity 2600