Back in 2012, it had ~ 18,000 weekly subscribers (excludes people buying from newsagents). As 70,710 attended games last weekend, the % of potential fans reached is ~ 25% (if their readership has held up or even extended).
Just imagine if the Torygraph/Grauniad/Smite could attract that percentage of their target readers (approx 13.5m Tory Voters, 12.9m Labour Voters 2.3m Liberal Voters at 2017 election) with their Sunday editions (278,500/163,700/712,300 respectively): they wouldn't be worrying about circulation figures if they could match The Rugby Papers catch.
But your point about the Slot Machine is valid. ;)
I'm impressed at your attempts, but that's not quite logically right as a comparison.
Sport England puts the number of people actively taking part in rugby once a week at 199,000 (2015), there are more than 340,000 registered rugby players in the country, and BT sport averages 345,000 viewers per match, not to mention the peak of 8.9m who watched the Wales v England 6 nations match on the TV.
So even we take a very low estimate and call it 250,000 people who might care about rugby every week - they're selling to less than 7%.
On a similar measure the Sun (1.4m), Mail (1.3m), Times (500k), are therefore hitting 23% of those Tories daily. Much more weekly.
But let's not even consider the fact that in the last election, 19% of Mirror readers were Tory voters and 30% of Sun readers voted Labour because it all gets too confusing....