fwiw, shortening the line is definitely NOT what needs to be done at all. Indeed, you probably don't have enough line.
What temperature this seltzer is going to be maintained at will help determine what should be done.
[edit] In the meantime, here's an example of a properly configured dispensing system, assuming seltzer held at 40°F and carbonated to 4 volumes of CO2 (which is fairly typical I believe).
First, referencing
our favorite carbonation table, find 40°F on the Y-Axis, and scan across that row to the closest entry to 4 volumes, then run up that column to find the required CO2 pressure to maintain the seltzer at 4 volumes of CO2 at 40°F. Which happens to be 29 psi.
Then, referencing
the only line length calculator worth using, plug in the 29 psi for the CO2 pressure, keep the default line ID of 0.1875", change the vertical distance from the middle of your keg to the faucet spout if the default 1.5 feet isn't close, change the flow rate if you must (I'd keep the 10 second pint myself), change the default FG to 1.000 or something close for the seltzer, and leave the tubing "roughness" number alone.
The magic number required is calculated to be almost 26' of 3/16" ID solid vinyl tubing (ala Bevlex 200, which has been pretty much the industry standard beverage tubing for decades). But if one wanted to cut down the line requirement, consider using 4mm ID EVABarrier tubing - or even their 3mm ID line...
Cheers!