As others have said, these are classic symptoms of aquaplaning. As the front wheels hit the puddle a wedge of water is forced underneath the front tyres and lift them off the road enough for the steering to go light. Worst case the rears lift as well you lose control completely.
Nothing to do with the steering geometry and everything to do with the incompressible nature of water. Any tyre will aquaplane if you are travelling fast enough (airliners can aquaplane on landing and they have relatively thin tyres for the weight), but wide tyres will plane at lower speeds as the weight loading per square cm on the contact patch is less, making it easier for the water wedge to form and because water cannot squirt out of the way so easily. Narrower tyres cut through the plane of water to the road surface more easily and require a higher speed to start to aquaplane. Light vehicle weight makes it worse, speed obviously makes it worse, tyres with a poor water dispersal design (including some off road tyres) make it worse, worn tyres make it much worse, a flat non-porous road surface makes it worse. The depth of water required to start aquaplaning depends on the tread pattern of the tyre (slicks will aquaplane on a few mm, a mud tyre might need 2 or 3 cm). Deep water obviously tends to slow the vehicle quickly enough that a stable aquaplane rarely forms.
Defenders run fine with 285s, but now you know your vehicle is more prone to aquaplaning just be cautious. Risk of widespread flooding today - stay safe.