Function PlayerTextDrawSetProportional appears to scale text spacing to a proportional ratio. Useful when using PlayerTextDrawLetterSize to ensure the text has even character spacing.
Function PlayerTextDrawSetProportional was added in 0.3e and will not work in earlier versions!

(playerid, PlayerText:text, set)
int playerid The ID of the player whose player-textdraw to set the proportionality of.
int text The ID of the player-textdraw to set the proportionality of.
bool set 1 to enable proportionality, 0 to disable.

Return Values:
This function does not return any specific values.

new PlayerText:MyTextDraw[MAX_PLAYERS];

MyTextDraw = CreatePlayerTextDraw(playerid, 100.0, 33.0,"Example TextDraw");
PlayerTextDrawSetProportional(playerid, MyTextDraw, 1);

Related Functions
The following functions may be useful, as they are related to this function in one way or another.