MP .474 purple cam
Actually you are right to a degree, LOL.
Depends on where you are considering duration changes. If you degree the cam, use a standard .050 lift, duration doesn't change at all.
If you take it at the retainer you will have a very minimal increase when going up in ratio. If you took a standard 1.5 SB you'd have .075 theoretical lift at the retainer when at .050 cam lift. Now take that same lift point at the retainer of .075 and divide it by the new 1.6 ratio. Your .075 lift requires, .046875, which makes duration slightly longer to each of those points on the lobe. It's really insignificant, maybe a degree or two at the most, yet it's there.