That right furnace obviously was small. Does the furnace cycle on discharge stat if running on high for that zone? Can't imagine there's a duct system big enough for what that 95% furnace will need to move. Or does the other damper open to bleed air to the main zone?
Inifnity doesn't use a discharge temp. It knows internally based on equipment what the minimum airflows are in each stage. For heat pump and AC, it also factor in outdoor temperature (system capacity) to determine comfort airflows.
If it's a 60k furnace, it only needs about 1020 CFM on high stage depending on static pressure. The Modulating 60k furance gets by with 970CFM on high stage and 40% capacity on low stage is just 330CFM. Low stage on a 2 ton heat pump is 300CFM minimum. But it prefers 370-490 depending on outside air temp based on my observations.
Yes, I'm a very very big Infinity fan... 2 systems in my house and can't wait to add zoning some day to one or even both of them.
That's one of the coolest downflow 2 zone installs I've ever seen.