Appropriate sizing of thimbles.

[smiling.shramana]

I am using 1/2" line for anchoring my old sailboat. I ordered 1/2" heavy duty thimbles for splicing an eye in the line assuming a 1/2" thimble goes with 1/2" line. The thimbles swallow the line. On spliced examples I've seen previously, the line sits a quarter of an inch or so above the lip of the thimble. On my new thimbles, the depth of the groove (where the line fits) is 1/2" so the line is flush with the lip of the thimble. Is this right? Is it because the thimble is a heavy duty one? What is the proper way to size a thimble to a line?
Thank you all for your help!!
Mike