Found it easy to travel to Espiritu Santo Delta and engage the gaggle of enemies at entrance to Los Humildes Reregrinos a bit to the east - from across the river to the north using the tier 40 DT HTI. First lined up shot didn't work however. So got them all alerted and with the arriving reenforcements all went to the south river blank en masse. Simply shot into the rather larger group. Got at least two on the first shot and then continued to just grind for some Tier points ...