So essentially, with MA play, if you can see their icon they are within range - to my knowledge. I would like to say this applies to range text as well, however it may be range text that is from the same field. I will dig a little deeper.
This thing is a bit confusing, not least because of recent changes.
First, there is the range voice channel.
Then, there is the good old Room text channel (#3), which has traditionally been misnamed 'range' text by large parts of the AH playerbase - but it never was one. This text can be read (only) by those coming from the same base, but works without any range limits (even across the map)
Third (to increase the confusion), HT recently added a real "Range" text channel (#7, dark purple). Text equivalent to the voice range channel, can be read by anyone in the vicinity. New players have it enabled by default, old players would have to enable it in their chat window settings.