Do not allow any header wrap on the EGT probe.Do not over wrap or under wrap the probe. The header cloth should be at least 1/8" + away from the probe. Neither Dynon nor Rotyax know the exact cause of the interrupted EGT signal. It works on millivolts so it doesn't take much. It has demonstrated that the cloth and the probe are not compatible and can cause EGT temps to flux as much as 125F and usually to the high side. The oil tank will not effect the EGT probe. The probe is inside the exhaust pipe at temps around 1300F-1500F. The oil temp of 215F won't have any effect and the probe would have to be in the oil itself.
An EGT spread of 80F can be very normal for some engines. It depends on several factors. Carb sync, probe placement, internal carb wear, air filter, ect...
An EGT temp with only a 15F spread is considered the same. EGT temps differ with throttle settings and will move up and down and closer or farther apart depending on the throttle settings.
Bottom line don't worry about an 80F spread unless you know you did something that effected the burn and can correct it.