I guess this isn't that straightforward, and I'm not an expert but here my justification
One of the interesting things though is grip doesn't just go up or down linearly with tyre pressure.
Every tyre has an "optimal grip pressure", and its not hugely high.
Increase the pressure beyond this and you reduce grip as well as adding sidewall stiffness, effectively increasing the suspensions stiffness.
Effectively stiffening the rear slightly while simultaneously reducing grip from the optimal pressure should reduce understeer.
At least thats my theory, it seemed to work for me but I'm open to argument in general
I also believe that increasing the pressure is more effective here than reducing the pressure to a lower than optimal pressure (the other alternative) since I believe lower pressure tyres would actually grip better when the ultimate scrubbing forces exerted on them are not that high.
e.g. the Rears can be very light under trailbraking.
You would also be effectively reducing the rear suspension stiffness at the rear (adding understeer).
Also softening the front tyre pressure effectively reduces the stiffness of the front slightly.
Of course the side wall may deform a little more, but can potentially be offset by increased traction (at least until the tyre overheats).
There are many competing factors at work here I think.
Lowering tyres pressure will defintely increase traction when available grip isn't that high, but can cause heavily stressed tyres to overheat and eventually lose grip (and in extremes come off the rim).
Heres the info from the Toyo Motorsport Tyres tyre pressure guidance section which clearly mentions to reduce understeer, reduce the front hot tyre pressure, and increase rear hot tyre pressure.
Obviously within a sensible window
Hot Inflation Pressures Guide:
Changing hot inflation pressures by small amounts ( 1-4psi ) can be used to fine-tune handling:
reduce rear axle hot inflation pressure
Increase Oversteer increase rear axle hot inflation pressure
Reduce Understeer reduce front axle hot inflation pressure
Increase Understeer increase front axle hot inflation pressure
(BTW Stevo unfortunately I don't have seperately adjustable bound/rebound dampers, they are combined in a fixed adjustment ratio, but yes my intent was just to increase the load on the slightly less grippy outside rear tyre.)