Alexa does have trouble with letters as all she hears is the sounds "tee vee".
When you use the full "grammatically correct" command "turn on the TV" Alexa recognises "turn on the" and immediately knows that you are using a Smart Home Skill.
It is built in, this is from the docs:
Interacting with the Smart Home Skill API
Note this phrase a user can speak:
User: Alexa, turn on the living room lights
“turn on the…” is a phrase recognized by Alexa’s built-in interaction model. Alexa recognizes that this is a request to turn on a light.
Here are some other observations I have picked up when looking into naming devices:
Use the brand name i.e. "turn on the Samsung TV"
Use full stops (aka periods). I know that when making custom skills you have to define acronyms in a particular way. Here is an extract from the docs:
Note that acronyms and initialisms are indicated using all caps. Alternatively, periods may be used to separate the letters. Using lowercase without periods (such as “fire hd”) may lead to unreliable recognition since the spoken form may not be correctly detected.
This means the spoken letters in the name in Harmony/Alexa should at least be in caps (TV) but you might find you have better results with "t. v.".
You will definitely get better results by extending the name somehow e.g. "television", "main TV", "Sony TV", "Flatscreen TV".
Or... try phonetic variations e.g. "tee vee" or "tea vee"