I honestly think that what is being picked up is the heat of Their power Systems. The reason why We see them with IR is that through conduction of that Heat - The Heat becomes part and parcel of the Craft throughout its structure by conduction of the Heat it produces while Operating.
I do beleive that what was said about cloaking devices is true but I think that - Again - It is part and parcel of the Power Systems They are using and the indirect effects of Their Power Systems have the effect of cloaking the Crafts due to the Systems being used for Powering them.
Electrons excited to 60% the speed of Light will cause the Nucleus of an Atom to destablize. As the Nucleus of the Atom trys to return to It's natural state - There is a transference of Power caused by the return to It's natural state. Now if this excitation is perpetuated continually - The Power from the Nucleus of the Atom attempting to return to It's natural state is thereby sustained and can be used by applicable Systems hooked up to It in the right way.
Now where does this Power come from ?
It comes from the 5th Dimension as the Nucleus of the Atom is using the 4th Dimension as Its Intial Torque position to garnish Zero Point Energy from the 5th Dimension. That said, if this draws Power from the 5th - Then the 5th or at least the Higher octaves of the 4th Dimension must be where the Power System has to reside in locality. Therefore again - Due to conduction of the Power Systems They're using and the hard-wired connection to the Crafts structure - This would then put the Craft actually in at least the 4th and likely the 5th Dimension for residence as a reality for It...
Again - Just a posit here as I'm trying to figure it out like the rest of You...