Currently investigating insanely odd mining results 2 cards one rig or 2x one card rigs seems 2x as many shares!!!!

So I'm very new to mining and just started for fun a week ago. I had 2 gaming PC's so I just ran them separately for the past 5 or 6 days both were yielding 6-8shares per min(each) today I decided I'm going to sell one of the PC's after cleaning it up/prep for sale. I pulled the GPU out and popped it into my other pc and it's current uptime is 35mins and I do see that the hash rate has combined exactly as expected it basically doubled but my shares per min are still 6-8!!!?? either I'm stumbling across a major wtf bonus moment or there is a variable worth of the shares based of difficulty. This is what I believe to be the case but I'm hoping for a little insight, specs are terrible I know but I have free hydro electricity so it's all profit baby. Anyways specs: T-Rex miner ravencoin rvn2miners bsmith pool 1xgtx970 4gb=1.5-2mhs 100w+/- 20 1xgtx980 4gb=1.5-2mhs @100w +/- 45