I’ve run similar exit/survey flows a while back and the biggest issue I kept hitting wasn’t volume, it was consistency of quality. On paper the EPC looks fine, but once you start segmenting by GEO/device you usually see a big drop-off in conversion after a few days.
Also worth tightening tracking on the back end, because a lot of “good” traffic ends up being soft clicks that don’t survive postback validation. Are you seeing any difference in CR between Tier 1 vs Tier 2 GEOs in your case?