Prince- We live about an hour and 15 mins apart! I also use the LG 9200. I have a new home now but a few years ago I had a raggedy ole trailer house that we used window units in. I saw temp swings like you are seeing but my biggest problem back then was too much humidity. My lack of knowlage drowned quite a few chicks.
Back to your question.... I think that that is an acceptable temp range. From all the reading I have done, you want a temp range of 101-102 for the still air bators. The 99.5 is the recommendation for forced air bators. I now have three temp guages going. Two digital ones and the little one that came with the bator. One of the digital ones has a tiny probe end that I put in an egg that I cracked a small hole in and filled with water and taped up. This one is giving me a constant temp of 100 deg. The two reading air temps are bouncing from 98 to 105. I stuck with the internal egg temp on my last hatch and had 34 of 37 make it.
Also, If you only have 12 eggs in, I recommend putting ceramic eggs or flat rocks in the bator to help with retaining heat when you open the bator up.
I hope my rambling will help!
Wayne