Yes, a bit subjective and it will vary if the primary cover is off or if pocking a finger through the inspection hole as on later cases. The way I do it through the inspection hole is 'can I actually move it up and down a bit?', which seems to work. So with the cover off I would say movement under a bit of pressure.
Perhaps the feel of the clutch can also be an indicator of too tight a chain. Although other things can cause clutch issues, with the lever pulled in does the centre turn smoothly or is it tight on the bearings?
It would be great if we could attach a spring balance (fishing type) and measure the ideal deflection by effort exerted then we could get a better idea of what it feels like.
Dave.