Look at it simply.
Check with the Authorities but I would expect that when the light spacing is 60m it is not mentioned because that is the standard spacing. It is only mentioned when the spacing is more than 60m.
If one assumes that in the absence of information in the AIP that the light spacing is 60m then one will always be safe because should the actual spacing be 90m you will be underestimating the RVR i.e. the RVR will be greather than you think it is because the lights are more than 60m appart.
eg you can see 10 lights - you assume spacing is 60m and think the RVR is 600m. If the actual spacing is 90m then the true RVR is 900m.
What does your operations manual say about the pilot assessment of visibility at these airports?
Seems to me that you are trying LVPs at uncontrolled airfields which is never a good idea!
Regards,
DFC