From what I’ve read it would seem that an author could be requested to write a synopsis from 2 to 25 pages, and it’s entirely at the whim of the agent or editor. Is this true? Does an author get asked to produce a synsopsis of a specific length depending on who is considering it? Or can I just write a good 2-5 pager and say: “take it or leave it.”
You've admirably toned down the language, but your question seems to be, I spent hours writing a five-page synopsis for Miss Snark, and she retired. Now I want to send my manuscript to Evil Editor, and the bastard wants a seven-page synopsis! If I have to write twenty different synopses for twenty submissions of the same crappy manuscript, I'll be spending longer on the synopses than it took me to write the damn book. Screw that. You wanna know what happens in my book? Read it!
Here's what to do. Write a 2/3-page synopsis, put it in the middle of your query letter, and send it to a few agents. If requests start rolling in, some of them will be for the manuscript or a partial. Send them what they want. Others will be for a partial and a synopsis. Those go in the trash, and rightfully so. They're from agents who are trying to get out of reading your book! Is that the attitude you want from someone you're hiring to represent you?
Now, if requests aren't rolling in, if only one agent shows the slightest interest in your book, and that agent wants a thirteen-and-a-half-page synopsis, hand-written in pig's blood on artist's canvas stapled to a piece of sheet rock, you have some shopping to do.