Unfortunately, bars aren't an accurate indicator of that. It's possible to drop calls with 5 bars, or to keep a call going for hours on a single bar.
There's lots of reasons for dropped calls. Sometimes it's a capacity issue, where a cell site is overloaded and calls from phone most distant to the cell site end up getting dropped (this is called "cell breathing"). Backhaul could also be at capacity. It could also be a scenario where the signal from the cell site to your phone is strong, but for whatever reason the cell site can't "hear" your cell phone as well. Or, a handoff from one cell site to another didn't go as planned, and the cell at the receiving end failed to complete the handoff (which is pretty much where the term "dropped call" comes from). And yes, it's possible to be perfectly stationary and the cell network might still hand you off from base station to base station, sometimes several times, and back and forth in a hot-potato fashion between two cell sites.
Which cell carrier are you with? Maybe you could complain to them and convince them offer you a microcell?