I use a ceramic heat emitter bulb to keep the heat steady day and night. It does not give off light, so it's great for night time. I use two GE 6500K 26watt spiral bulbs in dome lights plus the ceramic emitter during the day. At night I use the ceramic emitter and a black heat light 40watt bulb in a dome light. At one side-end of my 55 gallon I have a large heat matt on the outer side wall bc it's cool on that side. My temps range 78 to 80 degrees F consistently.

It sounds as though you have the right idea. 85 degrees is a bit to warm in that area.

A photo with labeling of where the temps are would be very helpful. Could you print out a paper copy of your tank photo and label the temps in the temp locations?