I was wondering if, since my left angle has about 3 degrees less of dorsiflex than the right, I could set the left boot with a different ramp angle or if they should be equal.
Ideally you are looking for symmetry, where the left turn rates and loading equals the right turn. Differences in dorsiflexion can cause asymmetry (and backseat skiing)---find a boot fitter knowledgeable in fore/aft balance and get this set up correctly.
You haven't really provided us with enough information to answer fully. Everyone suffers from a lack of muscular and bony symmetry but it doesn't necessarily mean a correction is necessary. Are you so tight the reduction of available dorsiflexion affects your skiing? For most the answer would be no. Most skiing does not require the full normal range of dorsiflexion and many boots once cold reduce the amount of dorsiflexion anyway.
Ramp angle affects stance and tip pressure. Certainly your stance and pressure should be the same left to right so if the "unhealthy" leg hinders your movement patterns corrections should be made but in your case almost certainly to both so that I would consider a heel lift under both feet and possibly toe lifts under the boots and/or toe pieces of both.
Thank you Lou, my right turns (pressure on left ski) are not as efficient as the left turns, but I have other issues going on including poor technique.
I'm not looking for an answer to my specific issues, too complicated and vague on the internet... but I understood that the idea is to have equal pressure/balance on both feet, and this could be achieved with an asymmetrical set up, but it's usually done by matching the "good" foot to the bad one.