The -1.1 NM is for the old analog signal on real channel 29. The digital signal on real channel 27 is stronger, but launches with an ERP of only 15 KW, definitely low power.
Getting even 4' of additional height may be significant.
If you choose to try adding an amp, (not my first recommendation) be sure to use an amp with resistance to overloading... The CPA-19, HDP-269 and 10G201 fit that requirement.
If the CS-2 has never seen more than a pixelated moments of reception, I would err on the side of caution when buying another antenna. I would opt for an 8-bay (DB-8, HD8800, CM4228 or U8000). I'd hate to hear you report the 4-bay can't quite do the job.
Would you add a rotator, or continue using the CS-2 plus the second antenna via an A/B switch? (A third option would be a UHF single channel combiner from TinLee.com and a forth option would be to use
network attached tuners.)