fontHeight not working in E.showMenu()

Hello Fellow Bangle.js Fans,

Novice Bangle.js app developer here, so please be kind. The default font used by E.showMenu() is a bit too small for me to read so I'm trying to increase its height. I tried setting the 'fontHeight' menuinfo attribute described on the "Graphical Menu" reference page, but it doesn't seem to have any effect. Changing the 'title' attribute does change the title so I think my code isn't completely wrong. If somebody would be kind enough to review my code below and tell me what I've done wrong I'd appreciate it!

var mainMenu = {
  "" : { "title" : "-- Main Menu --", 
        "fontHeight": 40, }, // no effect?
  "Item 1" : function() { undefined; },
  "Item 2" : function() { undefined; },
};

E.showMenu(mainMenu);