I found the best way with the M20 is to fill it from cold with the bleed screw open and just slowly fill it, giving it time to run through the rad and into the block. I can normally get almost ten litres in without even starting the engine.
Make sure the heater is set to hot and give all the pipes you can reach a squeeze especially the matrix feed. It will help prevent that getting an airlock if you park it facing uphill.
If you have an extra pair of hands to help fill the expansion tank to the brim then close the bleed screw while squeezing the very top hose as much as you can to push all the air out. when you let go of the pipe you should see the level drop in the tank.
Then the real test is to trun it on and watch it warm up. while doing that top up the tank if it drops then go for a spin to get the thermostat working a couple of times, then let it cool down and check the level again.
If you open the bleed screw again only do it with the engine running and at working temp with the filler cap in place

There is NO nucleus.