As of version 1.1.17, you have provided the option to set the roboport logistic radius to a custom value, for an easier or more difficult game, and as of 1.1.19, the default logistic radius is 25, which is the vanilla roboport logistic radius.

At present, however, the roboport construction radius is locked by the mod to 2 * logistic radius. Vanilla roboports, however, have a construction radius of 55, rather than 50 (as of Factorio 0.15.6, according to the wiki), in order to allow construction bots to construct roboports with isolated logistic networks.

Please consider either locking the construction radius instead to logistic radius * 2 + 5 (the simpler option), or (if you feel it would add to your mod) provide the additional option set a custom value roboport construction radius. Either option would allow for vanilla roboport logistic and construction ranges.