Ticks tend to hang around on the ends of vegetation around knee level. If you brush against, say, bracken, then you might pick up one or two ticks. If you lie down on short green grass, you're unlikely to find any ticks there. Ticks, on the whole, don't go wandering around looking for a feed... they hang around waiting for a feed to come to them! I spent many years just dossing on the ground without either a tent or a tarp for protection, and I NEVER picked up a tick. The only time I've ever come across ticks is when I've been brushing past stuff like bracken, and even then, only very rarely.
