I've got an HF4 from Gaps. Inlet tds 300ish, boosted pressure 68psi. Ratio 3:1, tds after RO 007
Had a problem with previous membrane which was distorted sealing ring (stainless steel housing) allowing unfiltered water to escape around the seal and contaminate the pure water.
Two points to remember:
1. If you don't flush regularly, or if your ratio is too low (less than 2 1/2:1) your membrane will clog up much sooner.
2. As you increase the ratio so you reduce the pressure at the membrane. You need to experiment to get the best combination