Gen 11 cooling System. Need advice/help

Today i swapped over all OEM radiator pipe work to corksport silicone.
Ran car to operating temp to open thermostat and turned both dials on heater to max 32deg, turned fan to max.
drained radiator into bucket and measured used fluid (close to 5 litres) only.Mazda spec is cooling system holds (7.5 lires)???????

Car was jacked up ,so maybe fluids still in water jacket and heater tank.
All new pipes fitted ,so filled system with clean demineralised water (5 litres) and lowered car ,ran engine 15 minutes to burp air and squeezed hoses, then drained all fluids again to flush system.
Again only 5 litres ,but full of green fluid.

Refilled system with fresh coolant.(5litres only) ??????? whats wrong ?????? it should have taken 7.5 litres as spec.??????
Any advice ,Thanks.

Id say there's just a bit of residual fluid you just cant get out of the system without some way of forcing it out under pressure.
I found the same thing with mine, I even dropped the car back down level with the radiator bung out to drain out as much fluid as possible, and it still didn't top up as much as the book stated.
Just keep an eye on the level over the next few driving cycles, I had to top mine up a bit.

Thanks MattMPS3, thought i may have had a air lock, Checked with Mazda today and found that the service techs very rarely get in excesss of 5 litres out of radiator. Water jacket seems to retain heaps.
Rule of thumb is that u should not mix coolants ,so it is very important that u flush engine and heater and radiator of as much old fluid .
Demineralized water is cheap ,so next time i will flush twice with clean water.