If it helps, I found this link with pictures of a Lenovo L440 fitting inside an S19 (no sleeve) - perhaps the L440 is close in size to the Lenovo laptop you are carrying?. It is also a good review comparison between the S19 and S25 volumes. It might be useful too to note that the S25 is basically the same volume as the Western Flyer you are thinking of too.
Synapse25 & Synapse 19 Tom Bihn Minimal Travel
Hope this helps
Cheers!