https://www.games2gether.com/endless-space-2/forums/66-game-design/threads/28306-missiles-can-t-get-through-flak-at-all?page=4#post-252221

https://www.games2gether.com/endless-space-2/forums/68-game-help/threads/29219-space-battle-guide-explanation-of-game-mechanics

Simulation/Battles/HullDefinitions[Terrans].xml

<!--  **   Terran Large Attack Hull   **  --> 

<Slot Name="Weapon01" ShowPositionMarker="true" PositionMarkerAngle="180">

<RestrictedModuleCategory>Weapon</RestrictedModuleCategory>

<RestrictedModuleCategory>Squadron</RestrictedModuleCategory>

<RestrictedWeaponType>Kinetic</RestrictedWeaponType>

<RestrictedWeaponType>Missile</RestrictedWeaponType>

<RestrictedWeaponType>Laser</RestrictedWeaponType>

<RestrictedWeaponType>Beam</RestrictedWeaponType>

<RestrictedWeaponType>KineticRailgun</RestrictedWeaponType>

<RestrictedWeaponType>BoardingPod</RestrictedWeaponType>

<LineOfSight>

<Direction X="1" Z="0"/>

<Angle>120</Angle>

<VisualSlotName>MDL_Wp_SmallSide_Right_00</VisualSlotName>

<VisualSlotName>MDL_Wp_SmallSide_Right_01</VisualSlotName>

<VisualSlotName>MDL_Wp_SmallSide_Right_02</VisualSlotName>

<VisualSlotName>MDL_Wp_SmallSide_Right_04</VisualSlotName>

</LineOfSight>

<LineOfSight>

<Direction X="-1" Z="0"/>

<Angle>120</Angle>

<VisualSlotName>MDL_Wp_SmallSide_Left_00</VisualSlotName>

<VisualSlotName>MDL_Wp_SmallSide_Left_01</VisualSlotName>

<VisualSlotName>MDL_Wp_SmallSide_Left_02</VisualSlotName>

<VisualSlotName>MDL_Wp_SmallSide_Left_03</VisualSlotName>

</LineOfSight>

<ModuleModifier>

<SimulationDescriptorReference Name="MultiplierX4"/>

</ModuleModifier>

<UISlotName>UIFrontRightWeapon02</UISlotName>

</Slot>

Simulation/Battles/SimulationDescriptors[ModuleWeapon].xml

<!--  Multiplying damage for ship size  -->

<Modifier TargetProperty="Damage" Operation="Multiplication" Value="$(Multiplier)" TooltipHidden="true"/>

<Modifier TargetProperty="MissileHealth" Operation="Multiplication" Value="$(Multiplier)" TooltipHidden="true"/>

So, based on these materials, I concluded that

1. Hull Size only affects the damage and health of each salvo and does not increase the number of salvos.

2. Equipping weapons on heavy slot also has the same effect with hull size. It will not increase the number of salvos.

3. Having kinetic weapon on larger hull will increase the number of flak turrets.

4. But having kinetic weapon on heavy mount will not increase the number of flak turrets, neither the damage of flak.

5. Turrets displayed on 3D-model are just decorative and does not actually mean there is more turrets and will fire more salvos.

However, I did not found any concrete evidence to prove those conclusions. Is there anyone who cross-checked on those things?