Another funny coolant system question

So I just fitted a Alloy radiator to my 94 B2200 (with a 2ltr Courier motor fitted) and noticed today when I got home that the top of the radiator is pretty hot and the bottom is barely luke warm.
It's not overheating (sitting on 1/4) so I'm mostly just curious as to why it wouldn't be the same temperature all over.

To help out people before anyone answers my question I will just make note of stuff I've replaced lately.

(All new): Full alloy radiator (Factory width and height, 2" deep, twin core with much larger tanks), headgasket, top and bottom hoses, 3x bypass hoses, thermostat, water pump, radiator cap, 12" electric fan and controller.

Not cooling related: inlet and exhaust gaskets, new Mazda Bongo Dizzy, leads, cap, rotor, igniter module, spark plugs, fuel filters, fuel pump, idler and tensioner bearings and cambelt.

Like I said it's not overheating, the heater is working great, but when I feel the hoses, all the bypasses and top radiator hose are hot and the bottom one is cold (and the pressure has built up).
Is it possible that the thermostat has suddenly died on me?
If so, why is the top hose and tank hot? wouldn't that make the whole radiator and hoses cold?

Apparently your brand new radiator is doing its job.

You might just have to top off the radiator. Once the thermostat opened the first time after you installed everything, the air bubble that may have been trapped behind the thermostat escaped. That would drop the level a bit, but even so, a radiator when it is working correctly, and in your case, a double core unit,
dumps a LOT of heat between the top and bottom.

So maybe everything is fine, and up to this point, you just learned a new fact in Mazda Fabledom.

I did think that too but I'm curious as to if it's possible that the thermostat is only partially opened?

About the only thing I've noticed that's different is the temp gauge, when I first start driving it used to climb up to about halfway then drop quickly to a quarter, now it just climbs up to a quarter and sits there.

I say youve done a great job on your cooling system. Sounds to me theres no problem.