Last Stand against Hive Fleet Typhon

3k of Scott's Tyranids vs 2k each of Chris' Astra Militarum and Aidan's Lamenters

Tyranids start with 18 CP, and generate 2 CP at the start of each of their command phases.

Lamenters and Guard both start with 12 CP, and each generate 1 CP in each of their command phases.

Table Setup and Deployment
Imperium designate two adjacent sides of the table as the "Tyranid Board Edge".

Imperium set up the terrain on the board to their best advantage. Maybe several buildings forming a sort of 'citadel' or fortress? There should be little terrain except craters around the Tyranid edges. Imperium puts down a single "Citadel and Extraction-Critical Objective" objective anywhere on the table.

Tyranids can deploy any number of units wholly within 6" of their board edges, or into normal methods of deep strike. Any number of units may be placed in strategic reserves for free.  For the purposes of bringing in strategic reserves, the other two non-Tyranid sides of the table count as "enemy's battlefield edge", and no area counts as "enemy deployment zone", which is to say, strategic reserves will always enter with the same rules on any turn: wholly within 6" of either Tyranid Board Edge, and more than 9" away from Imperium Units.

Imperium then deploy all their units anywhere on the table, or into normal methods of deep strike. In theory, Imperium could deploy directly into engagement range of Tyranid units (representing units who covered the retreat of the last Imperium defenders into the current stronghold), but that might be tactically unwise.

Tyranid player takes first turn, no seize attempt.

Tyranid Sustained Assault
At the end of any turn in which a Tyranid unit is destroyed, that Tyranid unit is put in the "Reinforcement" pool.

At the end of every Tyranid movement phase (so after reinforcements have been placed that turn), roll a dice for every Tyranid unit in the "reinforcement" pool:

On a 3+ Troops units move into Strategic Reserves, or some other form of deep strike organic to their rules.

On a 5+ Monster units move into Strategic Reserves, or some other form of deep strike organic to their rules.

On a 4+ Non-Troops Non-Monster units move into Strategic Reserves, or some other form of deep strike organic to their rules.

Named characters (Old One Eye) and special characters (Eater of History) never respawn.

Outcome
Tyranids win Major Victory if they have annihilated every Imperium unit on the table by the end of round 5.

Tyranids win Minor Victory if they hold the "Citadel / Extraction-Critical" Objective at the end of round 5.

Imperium win a Minor Victory if they hold the Citadel objective, and have resisted Annihilation at the end of round 5.

Imperium wins a Major Victory if they AT ANY POINT 'Table' the Tyranids (only counting units on the table top), so Tyranids should deploy so as the guarantee the question of being tabled never comes up.