Actually... High altitude... you just want a little less pitch. Lower pirch gives better low speed POWER. the engine is mre efficiently using the propeller at high rpm with low airspeed. This gets you off the ground better.

In general, RC aircraft have MUCH higher power:weight ratios than full scale.

They don't put a larger engine into a Piper Cub when it takes off from sea level and then flys up to its operating cieling of appx 12,000 ft (because the pilot need oxygen above there... the engine does not mind at all)

With the Piper Cherokee-6 (6 passenger 300 hp airplane) that my parents used to own... at high altitude they did a more careful weight and balance calculation... and verified the "density altitude"... then they cofirmed that the runway was long enough. NO OTHER CHANGES to the normal takeoff. (generally the airports they went to... it would have had to be 190 deg F and have the lowest barometer reading in history for the airport for the runway not to be long enough for full load take-off...)

Normal takeoff proceedure on the Cherokee was to set a specific ( in the low range of the variable ptich prop's capabilities) pitch and run the engine up to a specific rpm. No change for altitude.... just use more runway.