I don't think we understand each other.

To me, several times shorter makes perfect sense, and twice as short is a special case, where it is two times as short. Thus, several times shorter includes:

• two times shorter == twice as short
• 1.5 times shorter == 1.5 times as short
• five times shorter == five times as short
• several times shorter == several times as short (the "as short" construction sounds clunky to me here in this case)

As i write these out, i realize what you were trying to say: X times shorter is equivalent to X times as short for me, so equivalent that I didn't realize when I was using one or the other.

You are saying that for some people, the "X times shorter" construction doesn't sound natural. I can respect that, but it doesn't seem like a part of mainstream English to me at least.

"Twice shorter" isn't what anyone is talking about. That isn't how you combine the words, at least to me.