They like sunny spots in woods (even tiny ones from a single shaft of sunlight piercing a dense forest canopy); but they also venture around the edges of woods. They appear relatively disinterested in nectaring, but will feed from bramble when in flower. I expect other folks may have experience of them on other flowers.
So: if it has found its way to your garden, you are probably doing something right to encourage it already. The long grass sounds unusual; it may just have been resting in the shade down amongst the stems. However, the larvae are grass feeders, so the female might have been laying eggs. Wanting more of the same may be tricky however. They rarely occur in large numbers, partly because a male will defend his 'sunspot', sending itinerants off to find one of their own. Two's a fair target however: male and female.