No idea about the plastic box.
BlueNRG-2 supports BLE data length extension, which may have data payload up to 251 byte in one packet.
Decreasing 4-byte L2CAP header and 3-byte ATT Opcode, the maximum length of ATT data can be 244 bytes.
The maximum allowed ATT MTU is 65535, and the maximum characteristics size is 512.
To transmit a characteristics value of length longer than 244, the value has to be fragmented in multiple packets.
However, since notification is a single-packet event, 244 will be its limit.
