How to increase roads detail display

Hi,
I have BaseCamp 4.6.2 running on a Windows 10 laptop which I use for planning motorcycle routes which I then download to my ZUMO660 GPS. The map on BaseCamp and the GPS is City Navigator Europe NT 2001, unlocked. I live in Scotland which has a large number of minor country roads which I like to explore.

When viewing an area on the screen in 2D view in BaseCamp it displays the major roads connecting the large towns, and also the placenames of small town and villages apparently in the middle of open countryside, but none of the more minor roads going to these places. If I zoom in, the minor roads eventually appear, but to make the very minor roads appear I have to zoom in until the screen map shows only a very small, say 2 miles by 1.5 miles, rectangle (I get a 0.2mi scale indicator in the bottom right hand corner).

Is there any way to make the minor roads appear much earlier in the zoom sequence?

I would like to see ALL roads when the screen is displaying an area of about 20 miles by 15 miles, (with 2 mi or 3mi scale indicator in the bottom right hand corner), similar say to a 4 miles to the inch O.S. map.

I have tried altering the various settings in Edit...Options.., View, Tools and Map dropdown menus, but without being able to make any difference to the levels in the zoom sequence.