The 25% ingots spent part is not true.

Whenever a player makes a spin, be it ingot or free 20 coupons will be added to the pool, so it's 100% ingots spent + all the free spins.

Other than that, well it is possible that chances on getting coupons was lowered so that cashers who actually invested big amounts of money in this event would get some coupons for it. Dividing 5000 coupons between 20 players... well yeaaah.

Overall, a lot and lot of players received their 250 - 500 coupons, even on my small little server (though, I sadly was not one of them).

There is also a possibility that simply seed number moved so far from the coupon rewards, that it became nearly impossible to get there at the moment, and seeing the pool grow people started cashing more and more. IF this one is the case, some people will be VERY happy in few hours from now on :P