A simulcast system is just that, a simulcast system. Lets say you have 4 tower sites with Site 1 being the prime site. The prime site is where the other 3 sites are linked to. It does not matter where a subscriber is located within the coverage area. The subscriber is going to key up the nearest tower site and in return all 3 of the other sites will key up to simulcast the transmission. The user cannot control what tower they hit because that is not how a simulcast works. If it was a trunking system, that'd be a whole different story.
To put it simply, you, the user cannot select a tower site on a simulcast system. The system automatically decides what tower site is closest to you.