How does a federal tax refund work?

IRS Tax Refund Query by jQ: How does a federal tax refund perform? I have two W2's since I interned with my employer in two various states over the program of 2 semesters final year. If I enter the info for just 1 W2 (around $ 10K) into turbotax (and some other tax programs), it reveals a federal refund amount of $ 850, but if I add the 2nd W2 (also around $ 10K) the federal refund volume drops to $ 450. Is this appropriate? Should not the refund amount boost?