We also put the probe in an egg tub, usually a tub in the middle of the incubator. That way you just set the thermostat to the correct incubation temp.

Having it taped to the flexwatt and setting the thermostat to 98 to get the right temp in the egg box could lead to your incubator overheating and possibly loosing the clutch. Basically there is nothing stopping the flexwatt from heating the whole incubator to 98. What I would do is just set the Helix to 88 and put the probe in the egg tub at the same time. That way the Helix will now be sensing the temp in the egg box and since it will be programed to 88 it shouldn't cause a temp swing.