Water temps shouldn't make that much of a power loss especially at only three degrees of a difference , unless you have a dodgy map that suddenly tells the car to lean of the fuel when temp goes above 81
horsepower drops of rapidly with boost temps but not so much water temps
Does the car data log fuel injector usage
can you check again the boost temps again
you really need to get it on a set of rollers with a guy that's good at looking at data logging and seeing what's dropping of and loosing you power by comparing data from different sensors and seeing what's dropping off when say one sensor is giving a dodgy reading
I think useing renaultsport software is not the way to go