I am trying to do a simple linear wipe on text. I am noticing the linear wipe is based on the size of the whole composition instead of the size of the text layer. How do I fix this?
a text layer is actually a content inside a full frame blank layer and that's what's happening. even if you did set your text to be the full frame size, if you tried to scale the layer down you would see that render order is tricky and won't let you linear wipe the layer like you want. you should use other workflow solution like using a mask on the text and using the path property to reveal/hide or try using alpha matte/set matte for the text with a rectangle
All dynamically rasterized layers behave this way. You could write an expression to figure out the actual text bounding box and derive the percentages, but there are ultimately limits on the precision of the Linear Wipe effect that may make this not as precise as desirable, especialyl when the text is very small. A workaround would be to use pre-compositions, obviously.