Dear Neil ,i'ved done some experiment with this map,
1.first i'm install the map into Mapsources,
2.Transfer the map to Nuvi 2465 by using Mapsources with full map contained about 66 map inside included TOPO maps.
3.Found the same problem with "sinanaykan" ,which is my Nuvi 2465 cant read the detail of the map when zoom in,in my case i cant read the map of 'RIAU Island @ Tanjung Pinang ' while zoomed in to 5km,the other area was no problem
4.the solutions,- I deleted the " TOPO MAPS" first before " RESEND " the map onto my Nuvi 2465
5.Now my nuvi 2465 can read those whole map of this Navigasi.net map closely to 15 Meter.
6.hope this will help anybody facing the problem like me
7.FYI i'm using Navigasi.net V2.92,TQVM