Bob downline braking/s effectiveness is determined by a combination of blade area, and freewheeling rpm (the slower the freewheeling rpm, the more drag). Much of the problem is the fact that your 1.60, being a two stroke engine, tends to freewheel at a higher rpm than a four stroke engine like, say, a Saito 1.80 would. Four stroke engines have higher compression which can be felt when you try to flip either engine over by hand (2 stroke engines are easier to flip).

You've got the right prop on it already, and changing it would not help braking, and would cost you performance in other areas IMHO. At one time I had a 12 3/4 pound H9 Cap that had sterling performance with an OS 1.60 and I swapped in a Saito 1.80. On 25% nitro fuel, I still had performance for Intermediate class manuevers, but had noticeably better downline braking which allowed more constant speed manuevers, closing the gap with the "big" boys. This class of plane will never have that "put the brakes on" downline performance of the 1/3 scale and larger planes, though.