A well aligned 1.8m dish, especially a solid one, is certainly usable to receive most C-band FTA channels in southern Ontario but it won't receive everything. However in my experience, a mesh 1.8m dish is a bit worse than a solid one and only usable on non-weak transponders assuming there is no adjacent satellite interference.
For example on SES-1, you won't receive the 4020 H 28000 transponder no matter how hard you try due to sandwiched adjacent satellite interference from the neighboring Galaxy 16 @ 99W and AMC 1 @ 103W satellites using the same frequency.
As a 1.8m dish is not 2 degree compliant, your dish is actually receiving a bit of 99W and 103W even when aimed straight at 101W. This means that you are at the mercy of the uplinkers of each satellite with the frequencies they decide to use. Usually they try to play nice and avoid using a frequency already being used on an adjacent satellite but this is not always possible.
A 2.4m dish is the minimum C-band dish size that's 2 degree compliant and is what you should at least be using and will receive about 95% of the channels out there with North American on C-band. However, to reliably receive 100% of all North American C-band channels, a 3.0m dish is the minimum size required.
Now for Ku-band using the BSC621 on a 6 ft. dish, I suspect you need to align the LNBF on the scalar ring a bit more as Ku-band needs a more precise alignment compared to C-band. As you are already aimed at 101W C-band, I suggest you try receiving the 11820 H 20000 transponder which carries the Pentagon Channel now known as DoD news which is strong enough to be received on a slightly misaligned dish.
If you get no lock at all, try moving your dish actuator a bit to the east or a bit to the west to see if it comes in as you could be a bit off due to the adjacent satellite interference issue I mentioned above. Once you get a lock, first check your dish's elevation again by slightly pushing or pulling on the bottom of your dish to see if it improves. If it does then your dish is not 100% aligned yet so try to tweak the alignment using Ku-band transponders if possible as they will ensure a more precise alignment.
Also if you are still having Ku-band reception issues even if your dish is peaked then carefully adjust the skew (twist left or right inside the scalar ring) and especially focal depth (slide in or out inside the scalar ring) of your LNBF in order to maximize signal. Keep in mind that the peak focal depth adjustment could slightly differ between C and Ku-band based on the dish you are using so it's best to make a note of it or take a picture before making adjustments.
