As I've described in the past, signal level in respect to the bars is only a relative level indicator and should not to be used for comparison of different phones, even if from the same manufacturer but a different model/year. It's about as accurate as the gas gauge on your car and should be utilized in a similar fashion. For example, a half tank indication on one car may be completely different than a half tank on another car. There are many reasons why and within each reason are even more variations that add to the complexity...
Signal level bars represent a combination of two types of signals , 1X which is cellular voice and 3/4G which is cellular data. Your phone is receiving both a the same time and uses both for individual and combined purposes. Also the quality of the signal has an impact on performance so even the same signal level at different times and differing atmospheric or nearby interference conditions can result in significantly different performance.
Since it's a combination of two different signal levels, one signal (1X) could rise while the other (4G) drops and you wouldn't necessarily see a change in the number of bars displayed, yet you might see your data transmission speed reduce accordingly. Therefore the bars should only be used as a relative indicator of YOUR levels on THAT device at any given time. If you were to take two different phones and place them side by side, you may see identical bars but the actual performance of those two phones may be very different. In contrast, there is the possibility that the phones will show different signal level bars and yet may perform similarly, and it's even possible that the one with less bars may perform better.
We need to touch on dBm for a second so this will make sense...
The common method of determining actual signal strength is
dBm (sometimes
dBmW or Decibel-milliwatts), which is an abbreviation for the power ratio in
decibels (dB) of the measured power referenced to one
milliwatt (mW) as it comes off the antenna(s).
A power level of 0 dBm corresponds to a power of 1 milliwatt. A 3 dB increase in level is approximately equivalent to doubling the power, which means that a level of 3 dBm corresponds roughly to a power of 2 mW. For each 3 dB decrease in level, the power is reduced by about one half, making −3 dBm correspond to a power of about 0.5 mW. So in the case of the numbers you'll see on your phone (unless you're standing next to a tower), they will be indicated in a negative number that will typically fall in the ranges of about -60dBm or .000001mW (five zeros), representing 5 bars to about -110dBm or .00000000001mW (10 zeros), representing 0 bars (*lower numbers are better).
So on my phone right now at -94dBm in 1X the antenna(s) is/are receiving about .00000000039 milliwatts of power and at-105dBm in 4G, about .000000000031 milliwatts of power, together representing 3 bars. For further reference, if I shield my phone by covering to reduce the received signal levels the lowest dBm I've seen on my phone in 4G is 124dBm and 1X of 100dBm, and at that number the signal level bar was 1, then the 4G dropped off completely and the 1X went to 98dBm, but at that very moment the signal level bar jumped to 3. So in that case, the system was telling me that although I didn't have an 4G (or 3G), I had a moderate level of 1X so it used the signal bars to indicate ONLY the 1X signal level which is why it jumped to 3 from 1. It also appears from my tests that the weighting is greater towards the 3/4G signal level than the 1X, meaning when the 1X remains the same but 3/4G changes the number of bars will change more frequently than if the 1X changes while the 3/4G remain stable. This further explains why when 4G went away for me, the number of bars jumped so considerably yet the 1X signal level hadn't moved but slightly.
Second, the dBm used by each manufacturer to indicate the best possible level (typically 5 bars), and also the dBm used to indicate no usable signal level (0 bars), are respective to the specific radios installed and at what levels in dBm they will perform as specified by the radio manufacturer(s) and also as per the expected performance of the antenna(s) and cabling. A higher quality radio will perform better at a given dBm than a lower quality radio, and may even be able to perform at a signal level which is so low that another manufacturer's radio would fail. So to compare bars on a Samsung phone with that of an LG is not a fair comparison since they use different radios, since different manufacturers may use a different "ranges" and "incremental differences" of signal strength to indicate the 1 through 4 or 5 bars of signal level.
For instance, right now, my phone is showing 3 bars, but in the network type and strength shows -86dBm in 1X and -105dBm in 4G (*lower numbers are better). Yet if I watch it, I've seen it go down to -92 and -107, and the three bars continued to display. Then in a few moments, the signal levels went back up to -87 and -105, yet I saw the number of bars drop to 2. This means if one level went down (higher negative number), such as the 4G and the other went up (lower negative number), it may still show 3 bars and yet you may get less reliable 4G. At -95 and -120 I have only 1 bar.
So why all the technical mumbo jumbo? Well basically to debunk the idea that less bars on a newer phone means worse reception. It may or may not, depending on all of the factors mentioned above and many others.
:-* 
