On paper, a wide search radius sounds useful. In practice, water, ferries, traffic and work patterns matter more than a mileage figure.
Someone in Eastney may be only a few miles from someone in Gosport, but that short line on a map includes a harbour crossing or a much longer drive. Havant and Waterlooville sit outside Portsea Island yet can be straightforward by road or bus. Meanwhile, travelling across Portsmouth itself is usually manageable, even if the Eastern Road has other ideas at rush hour.
The useful question is not “How many miles away are they?” It is “Could we reasonably meet after work on a Wednesday?”
When browsing Portsmouth singles, look beyond the place name. Ask which neighbourhood they are in, how they normally travel and where they spend most of the week. North End, Cosham, Southsea and Gunwharf can all fit under “Portsmouth”, but two people’s routines may still point in opposite directions.
A good local profile helps with this without revealing a home address. Mention a broad area, such as Copnor or central Southsea, plus whether you are happy to meet elsewhere in the city. If you live in the immediate mainland ring, say how often you come into Portsmouth. That small detail saves both people from building plans around a journey neither wants to make regularly.