No alterations to the I.R. circuit but i had to cover the receiver leaving a 1.5mm hole (it did trigger with my finger but could not detect drops).
Drop size i have had down to 15 ms using this solenoid http://www.ebay.co.uk/itm/300716739350?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649
These transistors http://www.bitsbox.co.uk/transistors.html scroll down to 2N2222A
No more idea than you about right or wrong but it works.
Did you try program change?