The first Tyranid preview from the Warhammer Community is up getting right into what most Tyranid players are concerned about.... Synapse, Instinctive Behavior, and Shadow of the Warp.
via Warhammer Community
https://www.warhammer-community.com/2017/10/30/tyranid-codex-preview-synapse-instinctive-behaviour-and-the-shadow-in-the-warp-oct-30gw-homepage-post-2/
Tyranid Codex Preview: Synapse, Instinctive Behaviour and the Shadow in the Warp
The new Tyranids codex is one of the most radical updates the army has ever received, from the seven new Hive Fleet Adaptations to a range of tweaks to the army designed to make every option in the book feel powerful and viable.
The core of these changes is a new set of abilities, tweaked significantly from their Index versions to allow for more flexibility while still remaining true to the spirit of the army. You’ll find your Tyranid army is more manoeuvrable, more dangerous to enemy Psykers and even more resilient to Morale tests than ever before.
For starters, Shadow in the Warp now affects all enemy Psykers within 18″ as opposed to 12″, while Synapse works on all friendly units from the same hive fleet within 12″ rather than 8″.
While Synapse coverage is easier to achieve than ever, thanks to this boost in range, Instinctive Behaviour has been changed in order to be less punishing:
Firstly, Instinctive Behaviour only triggers when the unit in question is more than 24″ away from a Synapse unit. This allows you much more flexibility when moving your units, and essentially gives single-model units (like the Trygon) a 24″ Synapse range, as they don’t need to worry about Morale anyway!
Secondly, Instinctive Behaviour doesn’t force you to ONLY shoot or charge the nearest unit; instead, you suffer penalties to your charge rolls and shooting. This means that in the later rounds of the game, when the enemy may have crippled your Synapse coverage, you’ll still be able to maintain a level of control over your army.
In short, the Tyranids are no longer an army that depends quite so heavily on Synapse to win, and guaranteeing 100% Synapse coverage at all times is no longer completely necessary. Significantly, monstrous creatures that work best when operating away from the bulk of your army, like the Haruspex and Mawloc, are much more free to do so.