how to request multiple public image sizes from a field's filename?
But avoid … Asking for clarification,  

Really? What a joke! I hate this forum so much

There are a few things happening here. When you make a change to the field in the content type UI the imagecache is being manipulated/cleared. Changing the javascript manually does not do this so the path is not pushed through the system.

The easiest way to do this is to have separate fields for each size in the content type to make them available to your js. Hide the display of the fields not needed on the page (use  hook_alter or the admin UI). 

Then in your js call them programmatically. To ease the JS call I would name the fields so they can be iterated, ie. field_photo_1(lrg),field_photo_2(med),field_photo_3(sml)