The Tyranid
FAQ says otherwise...
Q: If a model with Lash Whips is attacking a model with an Initiative-boosting rule/piece of wargear (e.g. Furious Charge, an Eldar Banshee Mask etc.), which order are the Initiatives modified?
A: The Lash Whips will reduce an enemy model’s initiative to 1 before any other modifiers are applied. So, a model with Furious Charge that assaults a Tyranid with Lash Whips will strike at Initiative 2, and an Eldar with a Banshee Mask will strike at Initiative 10 in the first round of assault.
RAW it works differently, but apparently the gents at
GW decided that eldar need a bit of a boost vs the bugs