In using the Hoekje tone hole spreadsheet to determine the proper local cutoff frequency for each tone hole, I have noticed that it is only possible to get the first hole from the bottom to have the correct local cutoff frequency by making it considerably larger than any of the others.
The other five holes are no problem, but the first one is problematic unless you cheat a little bit on it.
Since no whistle in current production features an unusually large first tone hole, it’s a fair bet that it’s safe to cheat on that one… but how much?
Some makers choose to make the first tone hole the same size as the second, while others make it the same size as the fourth and fifth, and still others compromise and make it half way in between the two aforementioned sizes… but nobody makes it larger than any of the others.
Is the first tone hole somewhat exempt from the rules governing the local cutoff frequency, which should ideally be just above the top of the second register?
I have also noticed that without exception every tube made using Hoekje’s spreadsheet need to have the bell end slightly shortened after the tone holes are drilled, because the bell note is always a bit flat in relation to the other notes… I have no idea why this adjustment should be necessary, but it always is.
So all you whistle tech-heads band together with me, and let’s find the answers to these questions… I know there are lots of people besides me who would be interested in knowing them.
Hmm. I made a G flute accourding to their dimentions at the bottom of the page, but I didn’t bother with the spreadsheat calculations. It came out fairly decent, as far as I can tell, which I can’t. But the first hole wound up pretty much identicle in size to hole 2 and 3.
Looking at my whistles, it seems that the ones that play the easy c nat the best have a first hole pretty much identicle to the 2nd and 3rd.
That’s about all I can deduct with my meager reasoning abilities. I never was that strong in math. I have to depend on superstition, cursing, and the luck of fools for my calculations. I have gotten by though.
It would seem I DID wind up with a larger than usual first hole on the copper whistle I made, now that you mentioned it. I hadn’t even noticed that I’d done that. It was by the ready made dimentions on the page.
You need add closed hole correction to the spreadsheet.
Also, graph out Frequency vs Cutoff ratio (cutoff ratio = localcuttoff / frequency)
Or, send me a message I’ll send you my modified version of Hoekje’s spreadsheet.
Also, a new revision of TWCALC (Tin Whistle Calculator) is available on my website.
Where is this spreadsheet? 
Peter Hoekje’s version: http://homepages.bw.edu/~phoekje/acoustics/mahome.html
Pete Kosel’s modified version: http://www.cwo.com/~ph_kosel/dflute.zip