Kindly do note that SD Drop Rate for NSN remains relatively high even for an optimized network. It is the way the SD Drop counters are designed. SDR values around 1.5% are normal. (You must have noticed that TCH Drop Rate is lower. It is always like that with the standard NSN KPI formulae).
However, i still think the ratio of your radio drop is very high. Is your core part of NSN or some other vendor?