OK so to get an idea of 'WHAT' the temps actually are (without measuring his shell, not very accurate for enclosure temps to do it this way). Put a object like a rock (or book or something similar we use a pitcher of water) in the enclosure at the cool end. Wait 4 hours then measure the temp of that object?
Then you repeat in the center of the enclosure .....? Then you do the hot side ....? this will take at least 12 hours or 2 days to do BUT it will tell you what the actual temp is of a mass in your setup. Now based on those numbers tweek the setup to get your exact desired temp range. 94 on the high side and 74 on the low is actually a pretty good range depending on how long your tank is. If you have a 24 inch long enclosure that is a gradient of 20 degrees over 24 inches ..... as bout a big of a change as you would want. If your enclosure is only 16 or 18 inches and that is the gradient it's really not a very comfortable place for your tort. There needs to be spaces that are pretty consistent in temp without real big swings in temp within a few inches.