While I have read that Kodak TMY-2 has good reciprocity characteristics and the Fomapan films show very significant reciprocity failure; the ILFORD data sheets for HP5+, FP4+, and Delta 100 all seem to show the same reciprocity characteristics through a rather imprecise and limited graph.
A photo.net contributor has published a formula to calculate reciprocity failure of Delta 100 'Corrected time = 1.15567 x (Metered time)^1.4379'; however, I have seen little in way of comparison between HP5+, FP4+, and Delta 100. Does a lack of comparison indicate these films all have the same reciprocity characteristics, which seems unlikely...?
Howard Bond published an article on this with some very useful information. I believe it was Photo Techniques in 2003. I don't have a copy on hand, unfortunately.
It included Tri-X 400, Tmax 400, Tmax 100, 100 Delta, and HP5+. That was the old version of Tmax 400, of course.
Tmax 100 and 100 Delta were the most linear of the bunch. But TMY is two stops faster... HP5 and Tri-X were the worst performers. Another conclusion was that no compensation in development needed to be done, which is good news.
100 Delta and HP5 definitely did not have the same reciprocity characteristics, according to Bond's test.
You'll have to locate the article somehow.