Per PCT Spec Sheet, Gain for Drop Amp is actually 13-16 dB [typ. 14 dB]....but NF is a fairly POOR 4 dB. Whereas Spec Sheet for inexpensive, waterproof
CM3410 says Gain = 15 dB with typical NF Under 2.0....and has been TESTED to confirm NF and Excellent Overload Characteristics. I would recommend replacing the existing Amp to improve sensitivity by AT LEAST 2 dB....and with KNOWN High Resistance to Overload by your Local Stations:
Mast-Mounted Amplifiers and PreAmps for TV Signals are the SAME THING....waterproofed, intended to be mounted just below the Antenna, accepting power via the Coax. An OTA Distribution or "In-Line" Amplifier is similar, but typically is NOT Waterproofed. A "Drop Amp" is somewhat DIFFERENT, intended for use with CATV systems with much higher Channel Freqs (typ. 1002 MHz), and allows the REVERSE Channels (5-42 Hz) to pass thru from Cable Boxes back to the Cable Headend Equipment....but they also work for OTA Channels, which are a sub-set of the wider CATV Spectrum....some (like those mentioned here) accept Power either via COAX (with extra cost Power Insertion Module) or via a dedicated PWR IN Coax Port.
YES, you should use a 75-ohm Termination Resistor on every UNUSED Splitter Port [even better, select splitter to minimize Unused Ports]. Unterminated ports cause SWR Problems to OTHER ports....which can result in NULLS on particular Channels at SOME Drops and NOT at others, depending on whether the cable lengths are close to a multiple of 1/2-wavelength for that Channel. Using 75-ohm Termination Resistors is ALSO important to ensuring that the specified Port-to-Port Isolation is actually being provided...this (typical) 20+ dB Isolation provides important attenuation of the Tuner's Oscillator Leakage Signal from causing problems for ANOTHER Tuner connected to another port on that same Splitter.
I would guess the reason you chose to aim the Low-Gain [abt. 7 dbi in either Band], Hi-VHF/UHF RCA Antenna towards mostly weaker signals toward 358-deg (Magnetic), rather than the mostly stronger signals toward 172-deg (Magnetic) would be because it was necessary to receive the STRONGER CBS on Ch46 [towards 358-deg], rather than weaker CBS on Ch12 [towards 172-deg]. Which then begs the question as to WHY you needed ANY Hi-VHF capability, since CBS on weaker Ch12 would be a Duplicate....and PBS Ch8 would likely be Duplicate to one or more of the THREE stronger PBS Stations [incl. Ch35 towards 358-deg]....seems to me that using JUST a Higher Gain UHF Antenna would work better.....
ALTERNATIVELY, you would "probably" find that pointing UHF 4-Bay Bowtie Antenna towards mostly stronger signals [toward 172-deg] would provide better long term Reliability....but you would also need. fol. Medium Gain Hi-VHF Antenna to receive CBS on Ch12 [also toward 172-deg]....and fol. VHF/UHF Combiner:
[Stellar Labs Deep Fringe 12-El FD-Yagi]
BTW: We would be Very Interested in how well your current RCA Hi-VHF/UHF COMBO Antenna works when pointed towards 172-deg....you may be pleasantly surprised.....