Guards Mortar Battery BM-13 Katyusha and 138mm rockets performance in FOTR

Hy all
on FOTR rulebook I can't find the reference for the BM-13 rocket launcher (aka Katyusha), so I mutuated this from BGKursk (same unit name "Guards Mortar Battery")

Comparing the statements for the 138mm rocket in FOTR (last line of "medium guns" table) I found them different fron those for Kursk, allowing a penetration value of 8 (the same of the airborne version for the IL-2 fighter-bomber), far better than the 5 given in BGK and also higher than the values given for other land-born rocket shells (es: 280mm nebelwerfer has 6, same as the US 4,5"rocket)

Is that a typo?

Kind regards

M

I would use the "5" from Kursk, yes.

Thank you
So the"8" value is only for the air-ground version
M