Yeah; Lansweeper are pretty fixed and they don't publish a lot of details on how they derive them. I don't really blame them; it is kind of the 'secret sauce' that makes their product work the way it does. Trade secrets, and all. There are definitely ways they could improve the experience, though, particular when a device is 'discoverable' via different protocols (i.e. wmi vs. snmp vs. whatever secrets they may use).
In the meantime reporting probably is your friend. One good sample report is the 'Windows: Laptops and desktops list' report, which uses the following to distinguish between the two:
Case
When tblBattery.Win32_Batteryid Is Null Then 'Desktop'
Else 'Laptop'
End As [Desktop/Laptop]
There have been a lot of discussions about how to distinguish between servers vs. workstations; check out the winter challenge for a variety of suggestions. If you are just dealing with Windows systems, the tblComputersystem.Domainrole field is my go to. If you're dealing with a more varied install base things get murkier.