It is not the 'nose' but the fuselage that matter, particularly the wall that separate the 'nose' area from the rest of the body. It is the wall's dimensions. That is where the radar antenna is mounted. If this wall and radome volumn can accommodate a larger antenna, no problem installing the larger one.
There is an inverse relationship between antenna dimension and beamwidth, meaning the larger the antenna the smaller the beamwidth. The smaller the beamwidth the better the target resolutions, particularly when dealing with fighters who can turn bombers when necessary. The danger here is distance. For the average X-band fighter aircraft radar, at 100km for example, multiple targets must be separated by about 5km in order for the radar to distinguish them apart. Against aircrafts like the B-52 or the C-5 this separation is necessary. But against Tornados or Aardvarks or Strike Eagles? No problems deceiving the defenders by flying fully loaded and tight ala 'Thunderbirds' or 'Red Arrows'. Smaller beamwidth reduces, but not necessarily negate, this tactical advantage by the attackers. The 100-200 km distance is crucial as this is range is limited by fighter aircrafts' radars. This is why the F-14 and F-15 have such large antennas. But they can carry large antennas because they are large aircrafts to start.
Next issue is antenna mass, particularly when it is moving and moving under high g maneuvers. The actuating motors must be of the highest caliber in every aspects, from design to material to assembly. It must capable of sweeping the antenna against forces and keep the mass stable throughout its sweep range. The word 'against' here is important as the motors must have total control of the antenna's inertia regardless of whether the sweep direction is the same as the maneuver's direction, or not, and this can change in an instant in a fight. The greater this mechanical 'jitter' factor the greater the system's self induced noise. Not good when the pilot is fighting for his life and his nation's cause. A really really really bad antenna assembly will render the entire radar system worthless, flop around inside the radome and inducing unwanted forces into the fuselage, possibly sending the aircraft out of control. But this would be discovered, contracts canceled and heads lopped off, literally and/or figuratively, in the eval period.
