By the way, the reservation is for address 192.168.1.8.
You always want to assign a Static IP address that is isolated from the normal DHCP assignments of 192.168.1.2 through 192.168.1.10, for example.
Try assigning 192.168.1.25 or even 192.168.1.50 to the printer to separate it from the normal range of assigned addresses.
On my system I also miss several of the DHCP clients. The wireless ones are always listed, but part of the wired ones are missing. e.g. currently I see 2 wireless devices, my other airport in bridge mode and my current computer. My other computer (That is being used now), my network laser printer and my solar panel interface is missing. I never was able to figure out why some are listed and some not. For all I made a DHCP reservation in the past.
Presence has nothing to do with lease times as my printer is on 24/7. The lease time only makes that they are no longer listed after the lease ends and the client is not present. In my opinion at least all active computers should be listed there because they have active leases.