In order to achieve the wide gear range that our customers like, we set up many trikes with a 24 or 27-speed drivetrain. This results in a wonderfully useful band of gearing. The one element that results from this set up is the fact that your trike (any bike actually) does not like to be used in the small front chainring/smaller rear cogs combination - this is called "cross chaining".
We set up your trike in the Large/Large gearing combination to prevent derailleur damage in the large chainring. This means that with the Xseam you give us you can access all of your rear gears while in the large front chainring. This ensures that your derailleur doesn't break when you are shifting to a lower gear while in the large chainring.
Similar to this scenario is the small chainring/small cog combination. Trying to run the chain around these two small circumferences creates slack in the chain that overloads the rear derailleur and has the potential to do harm to your drivetrain. This is bad technique and should be avoided. That same gear ratio can be achieved in the middle chainring.
While getting accustomed to your trike, we encourage you to use the middle chainring from which you can access all the cogs on the rear cassette. When you need to go faster, use that big ring up front with the smaller cogs in the rear. If hills loom on the horizon, drop down into the smallest chainring and use the larger cogs in the rear. You should spend most of your time in the middle chainring.
Cross chaining is not exclusive to your trike. It should be avoided on any bike or trike. Never cross chain your gears!
If you need to adjust your boom length, check your chain before riding to make sure that it allows you to get into the proper gears with harming the rear derailleur.