Kegging Questions about Vols of CO2

So, I use the chart in Papazian's Homebrewer's companion to determine vols of Co2 along with temp and psi, etc.

My beer is at about 34 degrees - I can't get it any warmer this time of year in my garage . . . my kegerator is turned as high as it will go. Well, I have my psi set at about 14-15, but the CO2 level does not seem all that high. The beer is just about how I like it, but according to charts, I should have a bunch of CO2 in solution - more, in fact, that I tend to like. Is something wrong?

One more thing - the beer tends to seem more carbonated as I reach the bottom of the keg. Currently, I have two brand new kegs on and the carb level seems about perfect. The last gallon or so of the last two seemed very carbonated. I assume that his is due to the greater head space in the keg and more CO2 going into solution as a result.

Does this seem about right? If so, shouldn't I back off of the CO2 as the keg is emptied?

The ultimate amount of CO2 in the ale only depends on the pressure and temperature. Since your kegger isn't running much, there probably isn't much air circulation inside. How cold is it in the garage? If it going below 34F at night, bottoms of the kegs will be colder and absorb more CO2.