Thin air can dramatically affect how an RC airplane flies. The most common symptom is a lack of perceived power or thrust. This applies to both propeller driven aircraft and electric ducted fans, but the latter is more susceptible to thin air because of the fans' smaller diameter and enclosed position inside the aircraft instead of outside in the front like a standard propeller. The average altitude where most of our aircraft are tested by us and operated by our customer family is 0-1000 ft ASL (Above Sea Level).
If you live in higher regions, such as Colorado with its 5,000+ ft ASL altitude, we cannot predict how each model will fly in such thin air. To compensate for potentially higher throttle use, we would expect you will need to keep your initial flight times in the two minute range, at least during your CG and trim flights, to allow a safe enough margin to calculate your burn rate at your altitude. Add 20 seconds to your timer on each subsequent flights until you are landing consistently with ~20% capacity remaining.