Looking at all these thresholds (more points available than I expected)...personally I think the system is largely fine as it is for the "new Brentford" who do loads of aways and is going to pretty quickly going to catch up in points, in a few years, with those who've been going for a long time, but not doing loads of aways.
I think it's more of an issue for "new Brentford" who don't do many aways, since the TAPs for aways are much higher, and they could find it hard to catch up without going for a very long time. I guess the question is "should they catch up", at the expense of people who've been loyal for much longer, likely in lower divisions.
Perhaps continue to use the existing TAP tiers, but simply reserve 15% of away tickets, for a ballot, that goes to any member or ST holder, who didn't manage to purchase once the 85% are sold out. That way they all get a shot at a ticket. Without it being guaranteed.