Incubation temperature question

I've been letting my incubator run for the past few days trying to dial in the right temps and what not. I have a thermo/hydrometer in the egg tub as well as out of it. The one outside is reading 89-91 degrees but the one inside is only reading 86-88 degrees. Is this going to be a sufficient temperature for the eggs once they are in the tub?

If you can keep it at 88 that would be best

Ive had fluctuation before but generally between 88-90. Maybe more water bottles or keep temps more consistent or a fan. If your heat tape is at the bottom only or top only, might have to add more tape.

I'm using a natures spirit incubator so it has a fan. I'll just play with my t-stat until I get it to 89.