The Innova is filled through the reservoir hence the absence of a cap on the radiator itself.

No manufacturer uses "concentrated" coolant on an engine. Either it is the 'pre-mixed' (diluted in water already) variety or the one you dilute with distilled (the drinking kind) water. I have not seen the coolant of the Innova. Types of coolant are usually identified by their colors. Our Toyota uses the red kind. My Pajero has the green one. I'm not too keen on their differences but both have to be mixed 50/50 with water and both have ethelyne glycol in them.

It is normal for the engine to take in coolant from the reservoir during operation. But then again, it should return to the reservoir again once the engine is cold (stone cold). If not, your first suspect should be how well the cap seals against the reservior.