Assaulting through difficult terrain into ongoing combat

I have been looking in the BRB for a mention on charging into ongoing combat.
As example: during the same assault phase I would first charge in with a unit of Wyches into an enemy in cover. Secondly I would charge in Incubi (or any other unit without plasma grenades).

My question is, does the second unit still would strike at initiative 1 because they charged through difficult terrain?
My reading from the BRB says that you will always be slowed down in the fight sub-phase on the turn you have charged. Regardless if the unit is already locked in combat.

This feels off but I can't find the page where this is clarified.

Do you know the page?
Many thanks.

IF the incubi charge in the same turn the wyches charged (the first round of the wyches' combat) - they strike at ini 1

IF the incubi charge in the second turn of the wyches combat - they strike at normal ini.

OK, so it matters if the enemy unit was locked before the actual assault phase. Where can I find this ruling?

If this is true, Fearless Wyches got a whole lot more important.

As for now I only saw pinning or forcing a deliberate go-to-ground as a means to prevent Init capping by terrain.

Page 55 in bold under the disorganized/multiple combats charge section in the English rule book is where you can find what aurynn has explained.

Basically yes you can charge through and attack at full initiative as long as that unit charged the round after the wyches were lock in combat. So you need to wait a entire round before your incubi can charge into that combat so they dont suffer the initiative penalty.

Wyches cannot hold any dedicated close-combat unit for 2 assault phases and overwatch and can handle any non-dedicated close combat unit themselves. There is not really point in using wyches as combochargers.

Incubi are counterchargers or Devastator/Tac combatsquad decimators. For neither of these you need grenades...