You must be reading something wrong, you can't be submiting 8k shares in 1 minute.
8192 is the share diff in the example provided by NFW, no the 2^32 is correct, it is needed in the equation to "translate" share diff to hashrate.
....
fine, plot your numbers in the equation.
18×971×2^32/60
you get 1.25terahash
if your hashrate is indeed an exact 1terahash then it is not exactly 18 shares / min
you can use the same equation (basic math) you get =14.396 shares per minute.
clear?
Also, where did the number 8190 come from? Maybe it should be 8192 (2^13). But then, why 2^13?
8192 is the default starting diff that KanoPool uses. The minimum diff the pool allows is 432. As you submit shares over time that adjusts to whatever is needed to hit the 18 shares/min that his pool shoots for. Other pools probably aim for a different share rate.
As Mikey said, you cannot be submitting 8k shares/min - that would suck up too much bandwidth. The whole point to a pool setting a working diff is to keep the bandwidth to a reasonable level. Remember, a pool has hundreds/thousands of miner connected to it and cannot tolerate that kind of data usage from them all.