Nitro pour is half foam?

[jkatz419]

I've had a Nitro setup for a few months now and have used it with two kegs of stout. The third keg I put on it is an English pub style ale. When this pub ale pours I get a full glass of foam that then settles into about a half glass of beer and a half glass of dense foam. This pic is after ~2min of settling. The Stouts didn't so this, they were maybe 3/4 beer 1/4 foam. I've turned the serving pressure WAY down to just 12 psi on the pub ale, the stouts were served around 20 psi. If I try to serve at 30 psi like most people seem to recommend I get all foam. could the base beer be over carbonated? I carbed it up to about 1.8-2.0 and it was definitely less fizzy then my other normal CO2 kegs. Any ideas?

The image didn't want to embed so here's a direct link:
https://www.flickr.com/photos/39685365@N05/14686682117/