I assume that "hanging directly in the NAS" means that the copying process within the Synology NAS is done directly from SSD to SSD. If this is correct, then in the second case PC --> NAS we have a network with the corresponding protocol in between. With your specification of the transfer speed 110 MB/sec, I assume from the spelling that "megabytes/sec" are meant. If you have an Ethernet network between PC and NAS with a usual transfer rate of 100 Mbps (megabits/sec, where 1 byte = 8 bits) then you have a theoretical maximum transfer rate of 12.5 MBytes per second on your Ethernet. Ergo, your Ethernet network must be a Gigabit Ethernet with 1000 Mbps/s. With the corresponding losses due to the network protocol and any other activities on your network, 45 MB/s is not bad at all.