One of the biggest problems here in the mountains is VHF coverage. In some places 100 watts can’t get you anywhere. Radio Mobile online provides online tools to estimate and produce coverage maps, and from my experience are surprisingly accurate when used appropriately.
The maps below indicate the estimated coverage area. Yellow is a weaker signal, where you can typically expect noise and trouble establishing two way communication, specifically 1 µV (-107 dBm). Green are stronger signals are are areas where you should easily be able to talk on the repeater as well as access it via a handheld, specifically 71 µV (-70 dBm). The reason why there is such a gap between weak and strong is due to the vast differences in receiver sensitivity, noise, antenna setups. So if you are “in the green,” and have trouble getting into the repeater, it may not be because the map isn’t entirely accurate; the purpose isn’t to pinpoint mobile fluttering, but to be as a guide to where you should be able to establish communications.