icsw estimator is more sensible than that of iv estimator, as it incorporate more covariate information, such that the estimator might have higher variances. this is a general problem for ipw-style estimation. the problem is exaggerated when there is only a small population in certain strata and compliance rate is low.  one way to compromise it to winsorize the estimates, in this paper they set the threshold as =0.275. if compliance score for lower than 0.275, it is replaced by this value. bootstrap is also recommended in the entire process to reduce uncertainty(abadie 2002).