Here's what my take on all this from reading these forms for the last few months:
The reason why LTE tends to drop down so much compared to your eHRPD and 1x signal is because LTE is much more fragile, especially when it is being utilized on the higher high frequency band class 25 (1900Mhz) . Due to this your RSSI and SNR values tend to drop much lower more quickly when indoors. Your eHRPD and 1x signal also comes in on band 25 but the signal is not as vulnerable to propagation barriers like LTE is. I'm not entirely sure on the specifics of why, but I would think it is because LTE requires more data to be sent at faster rates, while for example 1x does not so propagation barriers impair that ability on LTE more so. I also know from experience that 1x on band class 26 (800Mhz) has excellent building penetration characteristics, so I would expect an LTE signal on BC26 to be just as good as your 1x signal on BC25.
That said when we obtain devices that are compatible with BC41 (2500Mz) the propagation characteristics will be even poorer than what we see now for LTE. However Clearwire towers are typically spaced even closer together than Sprint towers and Sprint plans on deploying additional BC41 equipment on their towers that don't already have it in addition to deploying small cells. (mini cell towers on power poles, fem to cell, etc) That should solve part of the problem with respect to the BC26 TD-LTE when we see full deployment.
I'm trying to get my hands on a Nexus 5 for when I go home to Chicago next week. I'll be hunting for LTE800 and TD-LTE! The maps on sprint.com show my house being in a "turbo" area for Sprint Spark, which means that I'll for sure have that sweet sweet TD-LTE with download speeds of 50 mbps! (hopefully)