Even though the manual states that with DETREND= PRICES the prices are "corrected by the average price slope", it does look like "end-point flattening" is actually used (plotting corrected prices shows that).

Would be great to be able to detrend by a linear regression.

What is end-point flattening?

Turning the curve so that the starting point and ending points are equal.

So you don't want them to be equal?

I do not want detrending to depend on a single (ending) data point.
I want to have an option to detrend based on an linear regression line - which seems a more robust approach.

Thanks, understood.