sequence of tenses in unreal conditionals

[constantinusphilo]

Here is a quote from The Arrow of Gold by Joseph Conrad:
Mr. Blunt's expression had grown even more indulgent if that were possible.

Shouldn't it be 'if that had been possible'?

 

[Tdol]

Not necessarily- Conrad is describing a universal truth about the limits of human expression.

 

[constantinusphilo]

I think this would be the only explanation possible.