Depending on which part of the world you fly, topping only visible moisture (visible either to the eye or the RADAR) does not guarantee topping turbulence. And, this also varies with the time of year (jet stream position) and topography.
For example, it is
uncommon to experience less than moderate turbulence when topping thunder clouds while crossing the Rockies during the spring or fall (especially in the springtime) unless you have at least 5000 feet above the cloud tops. There have been reports of severe turbulence under such circumstances with as much as 10,000 feet clearance. These storm types are associated with fast moving cold fronts with a high speed jetstream above.
In contrast, flying in the tropical climates allows less restricted flight. There, topping the visible clouds by 5000 feet will normally produce no more than light turbulence.
Following the manufacturer's recommendations or your company's SOP for the use of RADAR makes good sense. Prudent RADAR tilt management is essential. And, normally, airliners are unable to 'top' turbulence. (Athough they can many times top the moisture.) Therefore, most manufacturers recommend (Boeing, Airbus, Bendix, etc.) that airliners avoid trying to top a storm, but instead, recommend diversion around the storm. Unless you're in a one of these new, high-flying business jets, you cannot regularly top turbulence.
With regard to antenna tilt, I've seen too many pilots fail to point the antenna sufficiently downward. The new generation RADAR units have the auto-tilt, and I've found these to be spot-on. (These negate the cockpit discussion regarding proper antenna tilt.)
In answering the original question, the posted responses are correct. Antenna beam width is dependent on antenna size. (Antenna gain and beam width go hand-in-hand and are inversely proportional.)
Further, unless the 'Gain' control is set to MAX, most time the tops of the clouds will not paint. Even with the control set to MAX, many storms have insufficient moisture to really show much of a return. Again, refer to the above example of springtime over the Rockies. I've seen cases where the returns were relatively weak (due to lack of moisture), but we got the $%^% beat out of us due to the convective movement.
(Please don't misunderstand what I'm saying. I don't recommend flying around with the gain control in MAX. 99% of the time, the CAL (or NORM) position is the proper setting. I just mentioned the MAX setting to illustrate how little moisture can be in these cloud tops. Again, follow the SOP, and you can go a long way to protect yourself.)
One Axiom of RADAR use: Moisture does not necessarily equal turbulence. We all learn this (OJT) at some point.
PantLoad