I don't think a handheld antenna will help much. Even where I live high up, its all dependent on where the ambulance is. It goes from really strong signal to nothing. I also have a 125AT and find its quite good at receive.
I'm not sure of the repeater you mean though since at least in my city EMS just uses vehicle repeaters like the OPP do. So the repeater you are trying to hear is constantly moving around. I use a similar Watson antenna and I'm 100 feet up and still, all depends on where the ambulances are when they transmit. Its better than nothing I guess. : )