Nearly impossible to tell what the carbonation level is with that method, and it's hard to diagnose your issue without knowing the carbonation level. What carb level were you shooting for? 80/20 meaning 20% CO2? If that's the case, my best guess is that the blend you're using is way too low in CO2 for the carb level and temp of your beer. Even g-mix which is 25% CO2 is intended for very low carb levels and 2° colder than your serving temp. My suggestion would be to try increasing the pressure to compensate, but too much pressure will cause problems at the restrictor plate. Maybe try increasing a couple psi at a time until the pour gets overly foamy, and then back it off a little.
FWIW here's a useful set of calculators for serving with gas blends-
Beer gas is a lot more forgiving than 100% CO2 when it comes to serving pressure, but you still need to be somewhat close to the equilibrium pressure. Using the calculator above and guesstimating a carb level of 1.6 vol, you'd need ~68 psi serving pressure to maintain equilibrium. This is obviously way too high and would cause excessive foaming at the restrictor plate. Increasing the CO2 content of the blend to 30% brings the equilibrium pressure down to ~40psi. That's close to the limit of what most nitro faucets can produce a good pour at, but it's close enough that even if you had to lower the pressure to 35psi you shouldn't have any issues.