Prior to 1.72, Syntax 1 of say3D (_this say3D _sound) would use a default maxDistance of unlimited(?) if not specified in the related CfgSounds entry for the sound played.
After 1.72, it seems that this syntax plays with a maxDistance of approximately 100 Meters (based on testing with alternate syntax (_this say3D[_sound,_distance])
This may be an error, or it may be intentional. If intentional, can we please have documentation to this effect added to https://community.bistudio.com/wiki/Description.ext#CfgSounds and/or https://community.bistudio.com/wiki/say3D