I posted this elsewhere, but, in the interests of discussion will repeat here.
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I think the idea is for the MQ-25 to disappear off downrange with the F18 so the F18 can carry more ordnance to just outside the contested environment, top up with fuel, go do war type stuff in the contested environment and then come back out to refuel and head home with the tanker. Therefore, the Tanker has to keep a very low profile to avoid becoming a target and a known point for the F18s to return to.
I wonder, if you flew formation juuuust right with regard to the radar threat, you could actually decrease the RCS of the whole formation by using the MQ25 as a blocker/absorber.
ETA, so it has a kind of spade nose with a bevelled lower body (with what looks to be a retractable camera)and a smoothed double bubble type of upper forward fuselage. The big bay (weapons or fuel or sensors?) door doesn't have low RCS edge features like we're used to seeing and there doesn't appear to be any turbulator vanes at the front of the bay to help with separation. In fact, given the panel gaps on the lower body and wing root joint it doesn't look like a very low RCS vehicle from underneath.