Yeah, given your usual 48 hours was extended to 10-11 days I'd say your notion of overcarbing is likely the problem.
There's only so much CO2 dissolved in beer and the more you use making "head" the less left to hit the tongue.
Indeed "flat beer" from excessive foaming is one of the more frequent complaints with kegging.
A dispensing system should be "tuned" to allow the desired carbonation to be maintained at the desired temperature.
The "tuning" is typically done via line ID and line length (though "flow control" faucets can simplify that to a degree). But a solution that works ideally at, say, 11 psi, is probably going to start foaming with another 3 or more psi (ie: overcarbed keg).
You might reference
our favorite carbonation table to dial in your carbonation/dispensing process (pick your desired serving temperature on the Y-axis, run across that row to your desired carbonation level - expressed in Volumes of CO2 where 2.4 is typical for many ales - then run up that column to find the recommended pressure to hit and maintain that carbonation level.
Then use the recommended pressure to come up with a beer line length solution with
the only calculator worth using.
Put them together and you should have an ideal dispensing system...
Cheers!
