Yes. When I said 20, I was thinking like a Base Federation Cruiser. Obviously Frigates are going to have less sensor power than a Cruiser, unless they spend space that could have otherwise been used for weapons or other equipment for more sensor power. Klingons, for example, might forgo sensor power to get better targeting scanners. And obviously there isn't going to be SFB hexes, but there still is range that has to be figured.
Another thing I probably wanted to make a little more in depth is the relationship between the Cloak and the sensors. A more modern cloak would be harder to detect by a ship with older sensors, and a ship with top of the line sensors would be able to easier spot a ship with a cloak from 20 years prior.
Using the half detection size as a base. I think the formula should probably be... (second attempt... first one had an easy to achieve divide by zero error in it) IF C > 0; S+Sc/(C*2) Where S=Sensor Level, Sc=Scout (The value here should only be more than 1 if in the case of a Scout Cruiser or bigger, and then to a max of 2), C=Cloak Level. If there's no cloak, then just skip the entire line and figure detection normally. (Otherwise there's a divide by zero error too, I thought about eliminating the error, but it skews the power of the cloak too much I think) Also I need to edit the above post just a bit with regards to the cloak, the ship that is cloaked has their sensor range halved, not the ship looking for the cloaked ship.