All-

First time booking a skymiles reward ticket. i noticed it doesnt matter if you pick one way or round trip you dont get a discount on your miles so i have been watchign and the trip down flucuates between 25k and 32.5k miles but the trip back is only 17.5 miles. im wondering if i should book the trip back and keep watching the trip down to save some miles or if its better to book both the round trip ticket at the same time.

the 17.5k trip home only says one more ticket available at that mileage

any thoughts?