just play with it these days ,not sure if its right but u can take a try .
the room size and surround room size makes huge different . bigger numbers gives you more space feel but the sound a liittle lay back ....so it really depends the style of your speaker , some speaker high notes really sharp and forward ,i suggest to turn bigger number , if your speaker have thick voice ,then i will select around 0.5- 0.7 . becasue not only the space feel , the smaller number will let your high notes more sharp ,bright and close to you as well . so if u turn your room size really low , the space feel was less,so u need to go to the "DSP level" and turn it more untill you satisfy . this is fun and the setting of yamaha was really great .