I agree with all about not cutting tips of slicon nipple shields.  In our
practice, we have for several years used a little trick that seems to help .
 We cut a crescent moon shaped piece out of the floopy rim of the shield,
avoiding the firmer teat area.  Mother puts on the shield with the cut-out
facing toward the baby's chin.  When mom brings the baby in for latch-on, the
baby doesn't feel the plastic on his chin.  Some moms cut two crescents so
baby's nose doesn't feel the plastic either.  Doing this also avoids the
problem of plastic rim folding up and over baby's nose which happens with
some moms.  We have also used paper tape to hold the shield in place when
moistening the rim isn't enough.