[NTG-context] simple way to change value of 'x' in \tfx?

[jbf]

I have the following setup currently, involving:

\definefontfamily[mainface][rm][texgyrepagella][tf=file:texgyrepagella-regular.otf]
\setupbodyfont[mainface,11pt]
\setupbodyfontenvironment[default]  [em=italic]

\setupdelimitedtext[blockquote][style=\tfx, 
before={\blank\setupinterlinespace[line=2.4ex]},after={\blank}]

My publisher thinks the default scaling of 'x' (0.8) is too small for 
the blockquoted text, and asked if I could simply indicate 10pt for 'x'.

I tried by using the line:

\definebodyfontenvironment[default] [x=10pt]

but that did nothing to change things. I tried a few other possibilities 
as well, e.g. just adding the x=10pt after the em=italic declaration, 
but that didn't work either.

I'm sure there is a simple way to achieve what I want. Any thoughts?

Julian