This set of tutorials by Remy might help.

https://www.youtube.com/playlist?list=PLulP-cGMLxw4qTpXfilRHgbDUg8WvrEX2

Depending on the type of map you are making...

Dungeon style symbols are usually imported at 100 px per map unit

City symbols are usually imported at 40 px per map unit

Overland symbols are usually imported at 20 px per map unit.

So it really depends on what type of map and how big you want your shield.

It looks good either way, but I prefer the style without the shadows. It has more of an inked map flavour.

25 minute shout :)

The older styles don't have the sheet effects automatically turned on when you open them, but you can change that by checking the little box called "Effects are on when loaded" in the Display speed dialog. It just means that things are immediately clear the moment you open the map. That first screen shot was without effects - either that or so far zoomed out they were invisible. It really is the largest dungeon map I've ever seen.