In the first major study of the genre, Joshua Scodel shows how English poets have used the poetic epitaph to express their views concerning the power and limitations of poetry as a response to human mortality.
A useful study of the genre from the sixteenth to nineteenth centuries, Scodel's monograph paints a broad picture of how the epitaph changed as a result of political and religious unrest--namely, the English Civil War and later, the revolutionary periods of the mid-to-late 18th c. Post-Pope, Scodel argues, the epitaph was a spur to personal, lyrical lament, rather than continuing its earlier role as public panegyric meant to demonstrate social values and inspire the imitation of virtue. If you're undertaking an academic study of the epitaph, Scodel's book is required reading.