Height of sallies
There is no standard for the sally heights, however, I use a number of 66" (1.68m) from the floor (when the bell is up) to the bottom of the sally, and only rising to 69" (1.75m) for bells around the 20cwt mark, with 72" (~1.8m) for bells from about 40cwt upwards which generally have 3ft6 long sallies.
I have worked these heights out over quite a few years, looking at where people catch the sally when ringing and setting sally heights to accomodate the band. The average height of your ringers should be catching the sally in the middle of the sally when ringing (not when pulling off, where they might be lower down the sally) which allows the taller, and shorter of the band to also have the use of the sally when ringing.
With regards to garter hole positions I have a spreadsheet that I've worked out pulley heights and garter hole positions if you're having the effect of hard work or a short handstroke pull on your bell and also having sallies at significantly different heights when the bells are down if you'd like a copy (PM me). The first thing to check is the height of the pulley box below the wheel, an awful lot of bells, the pulleys are too far away from the wheel which makes the handstroke pull hard work and has the same effect with sally heights as though the gater hole is in the wrong position. Once you've checked your bell has an ~85-degree angle of rope sweep above the pulley box, the garter hole position can then be considered. (Greater than 90degree sweep has issues with handling too). The garter hole should be at 90 degrees from a line from the centre top of the pulley box to the centre of the bearing, and out. A garter hole that's 4" out gives a sally that's 8" different in height between up and down. My spreadsheet works it out from the top dead centre of the wheel around to where it should be.