I think I remember reading in the WinPEP manual that the accel height can be below the height of the tallest obstacle, providing that obs is sufficiently far away to allow the aircraft to be cleaned up and the climb to be continued at the improved gradient compared to the unclean condition.
WinPEP output shows a min and max accel altitude, which is always printed on my airlines performance page.
BPS for our Boeings just specifies an accel height, which for my company is usually 800' agl but of course dependent on a/d obs, and again is printed on the page.