Hopefully somebody else has an answer about the ratio, but...... I've heard reports about the mini gauges from DCC failing after a couple thousand kilometers. Maybe they have been good lately, I dunno.
For the cost of gauges and shipping, it might be worth sending Jason & Hermes an email asking if the situation has been solved.
Edit: Sorry, got ahead of myself. Have you thought about going digital? Acewell, Koso, DanMoto, etc?