Why is ed25519 batch verification faster?

I've read at a few sources that batch verification of ed25519 signatures are faster than verifying an equivalent amount individually.

Why is this?

Also, is there a closed form model of the rate of performance increase, percentage of time decrease, relative to batch size? If not, are there samples which describe the various derivatives of efficiency or percentage of time decrease relative to batch size? If not, can some general descriptions be made such as the percentage decrease in time is held constant per batch size or that there are diminishing returns, etc?

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Did you read this blog post: blog.cr.yp.to/20140323-ecdsa.html ? There are few lines explaining how a signature works on the ECC. –  ddddavidee May 4 at 17:44