Thanks Seamus for your very nice mention. I hope to see you at Stonehill. And Uncle Jaque is right on the money to direct Tom to chiffandfipple.com. There isn't a perfect way to mic a whistle, but all the posts say a few inches from the fipple which is absolutely correct. Of course, sound levels while playing in the upper register are of great importance to achieve balance.
I will share a secret since I am of the Joanie Madden school of Maximum Reverb (bless you Joanie). I have two effects pedals that I use. The signal comes from the mic (an Audio Technica dynamic) into a Boss BASS equalizer which boosts everything from 1000 hertz on DOWN since the low whistles do not have the "oomph" that the high ones have. Everything above 1000 should stay flat. Then out of the EQ and into a Boss Digital Delay/Reverb set to about "Luray Caverns". This gets me the Joanie/Cherish the Ladies kind of reverb that does make some folk cringe. However, it allows me to take St. Patrick's Cathedral with me in my gig bag.
All the best,