Quoted from Eskaybee:
I nailed the 4 HOTK shots and ram in less than 5 secs so perhaps the quicker you get those shots out, the higher your bonus round shots? Who knows, but what a rush! After HOTK I was at 10 bil. Finished the game with 11 bil lol.
I always felt that combo shots made in succession should be rewarded extra based on how quickly they are completed as well. Many combos allow for maybe 5 seconds or so between shots, or unlimited time if there are no other switch hits in between. I think combos made within 1 second between shots should be worth 5 times as much as those made within 5 seconds between shots.