So if Boris can sideline the Brexit Party and win the Brexit vote he can draw on approximately 50% of the electorate, which would guarantee a majority. Well that is the theory anyway. He will seek to portray all other parties as remainers either in principle or by default and as there will be at least 2, and generally more, such parties in any constituency he will seek to split the vote (Labour, Lib Dems, Greens, Change UK, Welsh Nationalists , etc). Also, he will rely on Corbyn's unpopularity in traditional northern working class areas.Why are people so confident in an increased majority win for Boris if he can persuade Farage to abstain from competing? Is the expectation that a large number of people (a large majority) will vote for Brexit again? Everyone knows this election will be essentially another referendum on Brexit
But all this depends on the Tories being able to define the election as a Brexit Referendum in all but name. Labour will attempt to frame it otherwise, eg, austerity, Boris Johnson's character, etc. Also, if they can force him to ask for a Brexit extension and have an election after that they will hope to bring the Brexit Party back into play and split the Brexit vote.
He is certainly giving this impression but how much of it is an election ploy is open to question. The more he can position himself as likely to embrace no deal the more he sidelines the Brexit Party and sucks up those votes. My guess is that if he should succeed in getting an overall majority he will most likely negotiate a deal - one not greatly different from the current one (but with some face saving changes) - perhaps a version of the original NI only backstop. If he is not dependent on the DUP he would be able to get that through.everyone also knows that if Boris wins he will pull the UK out deal or no deal. As a no deal looks almost certain if Boris is in charge then essentially a vote for the Conservatives is a vote to leave without a deal.