By the way, what's your real name?

I don't understand this structure:

-It must be difficult to accept so drastic a change.

Why not: a change so drastically or a so drastic change?

Does it mean: Debe de ser difícil aceptar un cambio tan drástico? or does it have another connotation beyond my perception?? haha

And also in my notes I have that the construction 'so drastic' is made up of one adverb + one adjective within an adjective phrase, right, but at the same time they all are inside a determiner phrase??? where the **** is the determiner?? haha

Thanks in advance

Will you have a look at 'la gramática'? I've just started a new thread finally!
Well, am off to study..